chore(tier): remove dead trailing_headers config from warm backends (#6762)

TransitionClient::new() in crates/s3-client/src/transition_api.rs computes
trailing_header_support = opts.trailing_headers && override_signer_type == SignatureV4,
but override_signer_type is hardcoded to SignatureDefault at construction
and never mutated afterwards, so the expression is always false regardless
of opts.trailing_headers. The resulting field also has no live reader: its
only reference is inside PutObjectOptions::validate() in
crates/s3-client/src/api_put_object.rs, which is itself
#[allow(dead_code, reason = "MinIO-parity ... no caller in this port")],
and even there the reference to trailing_header_support is commented out.

So trailing_headers: true in the seven warm_backend_*.rs constructors has
never had any effect on request signing or chunked/trailing-header
behavior (stream_sha256 signing is gated separately by
metadata.stream_sha256 && !self.secure). Remove the misleading dead
configuration from the seven provider constructors so it doesn't look
like intentional, load-bearing behavior to future readers.

Found during adversarial self-check while implementing rustfs/backlog#2040 (out of that issue's scope).

crates/ecstore/src/services/tier/warm_backend_aliyun.rs

@@ -68,7 +68,6 @@ impl WarmBackendAliyun {
         let opts = Options {
             creds,
             secure: u.scheme() == "https",
-            trailing_headers: true,
             region: conf.region.clone(),
             bucket_lookup: BucketLookupType::BucketLookupDNS,
             ..Default::default()

crates/ecstore/src/services/tier/warm_backend_azure.rs

@@ -68,7 +68,6 @@ impl WarmBackendAzure {
         let opts = Options {
             creds,
             secure: u.scheme() == "https",
-            trailing_headers: true,
             region: conf.region.clone(),
             bucket_lookup: BucketLookupType::BucketLookupDNS,
             ..Default::default()

crates/ecstore/src/services/tier/warm_backend_huaweicloud.rs

@@ -68,7 +68,6 @@ impl WarmBackendHuaweicloud {
         let opts = Options {
             creds,
             secure: u.scheme() == "https",
-            trailing_headers: true,
             region: conf.region.clone(),
             bucket_lookup: BucketLookupType::BucketLookupDNS,
             ..Default::default()

crates/ecstore/src/services/tier/warm_backend_minio.rs

@@ -68,7 +68,6 @@ impl WarmBackendMinIO {
         let opts = Options {
             creds,
             secure: u.scheme() == "https",
-            trailing_headers: true,
             region: conf.region.clone(),
             ..Default::default()
         };

crates/ecstore/src/services/tier/warm_backend_r2.rs

@@ -68,7 +68,6 @@ impl WarmBackendR2 {
         let opts = Options {
             creds,
             secure: u.scheme() == "https",
-            trailing_headers: true,
             region: conf.region.clone(),
             ..Default::default()
         };

crates/ecstore/src/services/tier/warm_backend_rustfs.rs

@@ -65,7 +65,6 @@ impl WarmBackendRustFS {
         let opts = Options {
             creds,
             secure: u.scheme() == "https",
-            trailing_headers: true,
             region: conf.region.clone(),
             ..Default::default()
         };

crates/ecstore/src/services/tier/warm_backend_tencent.rs

@@ -68,7 +68,6 @@ impl WarmBackendTencent {
         let opts = Options {
             creds,
             secure: u.scheme() == "https",
-            trailing_headers: true,
             region: conf.region.clone(),
             bucket_lookup: BucketLookupType::BucketLookupDNS,
             ..Default::default()