netty: Remove obsolete HPACK encoder migration TODO

The encoder now uses 64 buckets, matching the Netty default, so migrating
to Http2FrameCodecBuilder no longer requires custom encoder injection
for the bucket count.

Co-Authored-By: Xirp Agent (gpt-6.1-sol) <xirp-agent@users.noreply.ghe.spotify.net>

Author: petedmarsh

netty/src/main/java/io/grpc/netty/NettyClientHandler.java

@@ -175,8 +175,6 @@ static NettyClientHandler newHandler(
     Preconditions.checkArgument(maxHeaderListSize > 0, "maxHeaderListSize must be positive");
     Http2HeadersDecoder headersDecoder = new GrpcHttp2ClientHeadersDecoder(maxHeaderListSize);
     Http2FrameReader frameReader = new DefaultHttp2FrameReader(headersDecoder);
-    // TODO: Add support upstream in Netty for injecting a custom Http2HeadersEncoder subclass
-    // into Http2FrameCodecBuilder before migrating to that API.
     Http2HeadersEncoder encoder = new DefaultHttp2HeadersEncoder(
         sensitivityDetector(neverIndexedMetadataKeys), false, 64, Integer.MAX_VALUE);
     Http2FrameWriter frameWriter = new DefaultHttp2FrameWriter(encoder);