Remove unused netty-codec-http dependency

Since we replaced all Netty header constants with string literals,
the explicit netty-codec-http dependency is no longer directly used.
AsyncHttpClient brings in the required Netty dependencies transitively,
and the Netty BOM in dependencyManagement ensures they're all at
version 4.2.7.Final.

This resolves the Maven dependency analyzer warning about unused
declared dependencies.

Author: claude

pom.xml

@@ -860,11 +860,6 @@
       <artifactId>async-http-client</artifactId>
       <version>${asynchttpclient.version}</version>
     </dependency>
-    <dependency>
-      <groupId>io.netty</groupId>
-      <artifactId>netty-codec-http</artifactId>
-      <version>${netty.codec.http.version}</version>
-    </dependency>
     <dependency>
       <groupId>org.playframework</groupId>
       <artifactId>play-ahc-ws-standalone_${scala.version}</artifactId>