Review fixes for jetty-12.0:javaagent (#18087)

Co-authored-by: otelbot <197425009+otelbot@users.noreply.github.com>

Author: otelbot[bot]

instrumentation/jetty/jetty-12.0/javaagent/src/main/java/io/opentelemetry/javaagent/instrumentation/jetty/v12_0/Jetty12ServerInstrumentation.java

@@ -53,7 +53,7 @@ private AdviceScope(Context context, Scope scope) {
       }
 
       @Nullable
-      public static AdviceScope start(Object source, Request request, Response response) {
+      public static AdviceScope start(Request request, Response response) {
         Context parentContext = Context.current();
         if (!helper().shouldStart(parentContext, request)) {
           return null;
@@ -76,10 +76,8 @@ public void end(Request request, Response response, @Nullable Throwable throwabl
     @Nullable
     @Advice.OnMethodEnter(suppress = Throwable.class, inline = false)
     public static AdviceScope onEnter(
-        @Advice.This Object source,
-        @Advice.Argument(0) Request request,
-        @Advice.Argument(1) Response response) {
-      return AdviceScope.start(source, request, response);
+        @Advice.Argument(0) Request request, @Advice.Argument(1) Response response) {
+      return AdviceScope.start(request, response);
     }
 
     @Advice.OnMethodExit(onThrowable = Throwable.class, suppress = Throwable.class, inline = false)