chore: remove legacy wsconncache (#11816)

Fixes #8218

Removes `wsconncache` and related "is legacy?" functions and API calls that were used by it.

The only leftover is that Agents still use the legacy IP, so that back level clients or workspace proxies can dial them correctly.

We should eventually remove this: #11819

coderd/workspaceapps/proxy.go

@@ -65,14 +65,9 @@ var nonCanonicalHeaders = map[string]string{
 type AgentProvider interface {
 	// ReverseProxy returns an httputil.ReverseProxy for proxying HTTP requests
 	// to the specified agent.
-	//
-	// TODO: after wsconncache is deleted this doesn't need to return an error.
-	ReverseProxy(targetURL, dashboardURL *url.URL, agentID uuid.UUID) (_ *httputil.ReverseProxy, release func(), _ error)
+	ReverseProxy(targetURL, dashboardURL *url.URL, agentID uuid.UUID) *httputil.ReverseProxy
 
 	// AgentConn returns a new connection to the specified agent.
-	//
-	// TODO: after wsconncache is deleted this doesn't need to return a release
-	// func.
 	AgentConn(ctx context.Context, agentID uuid.UUID) (_ *codersdk.WorkspaceAgentConn, release func(), _ error)
 
 	ServeHTTPDebug(w http.ResponseWriter, r *http.Request)
@@ -548,18 +543,7 @@ func (s *Server) proxyWorkspaceApp(rw http.ResponseWriter, r *http.Request, appT
 	r.URL.Path = path
 	appURL.RawQuery = ""
 
-	proxy, release, err := s.AgentProvider.ReverseProxy(appURL, s.DashboardURL, appToken.AgentID)
-	if err != nil {
-		site.RenderStaticErrorPage(rw, r, site.ErrorPageData{
-			Status:       http.StatusBadGateway,
-			Title:        "Bad Gateway",
-			Description:  "Could not connect to workspace agent: " + err.Error(),
-			RetryEnabled: true,
-			DashboardURL: s.DashboardURL.String(),
-		})
-		return
-	}
-	defer release()
+	proxy := s.AgentProvider.ReverseProxy(appURL, s.DashboardURL, appToken.AgentID)
 
 	proxy.ModifyResponse = func(r *http.Response) error {
 		r.Header.Del(httpmw.AccessControlAllowOriginHeader)