ci: remove dylib build pipeline (#22592)

## Summary

The macOS `.dylib` is only used by Coder Desktop macOS v0.7.2 or older.
v0.7.2 was released in August 2025. v0.8.0 of Coder Desktop macOS, also
released in August 2025, uses a signed Coder slim binary from the
deployment instead.

It's unlikely customers will be using Coder Desktop macOS v0.7.2 and the
next release of Coder simultaneously, so I think we can safely remove
this process, given it slows down CI & release processes.

## Changes

- **Makefile**: Remove `DYLIB_ARCHES`, `CODER_DYLIBS` variables and
`build/coder-dylib` target
- **scripts/build_go.sh**: Remove `--dylib` flag and all dylib-specific
logic (c-shared buildmode, CGO, plist embedding, vpn/dylib entrypoint)
- **scripts/sign_darwin.sh**: Remove dylib-specific comment
- **CI (ci.yaml)**: Remove `build-dylib` job, artifact download/insert
steps, and `build-dylib` dependency from `build` job
- **Release (release.yaml)**: Remove `build-dylib` job, artifact
download/insert steps, and `build-dylib` dependency from `release` job
- **vpn/dylib/**: Delete entire directory (`lib.go` + `info.plist.tmpl`)
- **vpn/router.go, vpn/dns.go**: Clean up comments referencing dylib

The slim and fat binary builds are completely unaffected — the dylib was
an independent build target with its own CI job.

_Generated by mux but reviewed by a human_

.github/workflows/release.yaml

@@ -58,87 +58,9 @@ jobs:
 
             if (!allowed) core.setFailed('Denied: requires maintain or admin');
 
-  # build-dylib is a separate job to build the dylib on macOS.
-  build-dylib:
-    runs-on: ${{ github.repository_owner == 'coder' && 'depot-macos-latest' || 'macos-latest' }}
-    needs: check-perms
-    steps:
-      # Harden Runner doesn't work on macOS.
-      - name: Checkout
-        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
-        with:
-          fetch-depth: 0
-          persist-credentials: false
-
-      # If the event that triggered the build was an annotated tag (which our
-      # tags are supposed to be), actions/checkout has a bug where the tag in
-      # question is only a lightweight tag and not a full annotated tag. This
-      # command seems to fix it.
-      # https://github.com/actions/checkout/issues/290
-      - name: Fetch git tags
-        run: git fetch --tags --force
-
-      - name: Setup GNU tools (macOS)
-        uses: ./.github/actions/setup-gnu-tools
-
-      - name: Switch XCode Version
-        uses: maxim-lobanov/setup-xcode@60606e260d2fc5762a71e64e74b2174e8ea3c8bd # v1.6.0
-        with:
-          xcode-version: "16.1.0"
-
-      - name: Setup Go
-        uses: ./.github/actions/setup-go
-
-      - name: Install rcodesign
-        run: |
-          set -euo pipefail
-          wget -O /tmp/rcodesign.tar.gz https://github.com/indygreg/apple-platform-rs/releases/download/apple-codesign%2F0.22.0/apple-codesign-0.22.0-macos-universal.tar.gz
-          sudo tar -xzf /tmp/rcodesign.tar.gz \
-            -C /usr/local/bin \
-            --strip-components=1 \
-            apple-codesign-0.22.0-macos-universal/rcodesign
-          rm /tmp/rcodesign.tar.gz
-
-      - name: Setup Apple Developer certificate and API key
-        run: |
-          set -euo pipefail
-          touch /tmp/{apple_cert.p12,apple_cert_password.txt,apple_apikey.p8}
-          chmod 600 /tmp/{apple_cert.p12,apple_cert_password.txt,apple_apikey.p8}
-          echo "$AC_CERTIFICATE_P12_BASE64" | base64 -d > /tmp/apple_cert.p12
-          echo "$AC_CERTIFICATE_PASSWORD" > /tmp/apple_cert_password.txt
-          echo "$AC_APIKEY_P8_BASE64" | base64 -d > /tmp/apple_apikey.p8
-        env:
-          AC_CERTIFICATE_P12_BASE64: ${{ secrets.AC_CERTIFICATE_P12_BASE64 }}
-          AC_CERTIFICATE_PASSWORD: ${{ secrets.AC_CERTIFICATE_PASSWORD }}
-          AC_APIKEY_P8_BASE64: ${{ secrets.AC_APIKEY_P8_BASE64 }}
-
-      - name: Build dylibs
-        run: |
-          set -euxo pipefail
-          ./.github/scripts/retry.sh -- go mod download
-
-          make gen/mark-fresh
-          make build/coder-dylib
-        env:
-          CODER_SIGN_DARWIN: 1
-          AC_CERTIFICATE_FILE: /tmp/apple_cert.p12
-          AC_CERTIFICATE_PASSWORD_FILE: /tmp/apple_cert_password.txt
-
-      - name: Upload build artifacts
-        uses: actions/upload-artifact@b7c566a772e6b6bfb58ed0dc250532a479d7789f # v6.0.0
-        with:
-          name: dylibs
-          path: |
-            ./build/*.h
-            ./build/*.dylib
-          retention-days: 7
-
-      - name: Delete Apple Developer certificate and API key
-        run: rm -f /tmp/{apple_cert.p12,apple_cert_password.txt,apple_apikey.p8}
-
   release:
     name: Build and publish
-    needs: [build-dylib, check-perms]
+    needs: [check-perms]
     runs-on: ${{ github.repository_owner == 'coder' && 'depot-ubuntu-22.04-8' || 'ubuntu-latest' }}
     permissions:
       # Required to publish a release
@@ -320,18 +242,6 @@ jobs:
       - name: Setup GCloud SDK
         uses: google-github-actions/setup-gcloud@aa5489c8933f4cc7a4f7d45035b3b1440c9c10db # v3.0.1
 
-      - name: Download dylibs
-        uses: actions/download-artifact@37930b1c2abaa49bbe596cd826c3c89aef350131 # v7.0.0
-        with:
-          name: dylibs
-          path: ./build
-
-      - name: Insert dylibs
-        run: |
-          mv ./build/*amd64.dylib ./site/out/bin/coder-vpn-darwin-amd64.dylib
-          mv ./build/*arm64.dylib ./site/out/bin/coder-vpn-darwin-arm64.dylib
-          mv ./build/*arm64.h     ./site/out/bin/coder-vpn-darwin-dylib.h
-
       - name: Build binaries
         run: |
           set -euo pipefail