Remove not needed null check (#11303)

Motivation:

throw exception if there is no method, it never is null, condition is always true

Modification:

remove unnecessary condition

Result:

cleanup

transport/src/main/java/io/netty/channel/ChannelHandlerMask.java

@@ -179,7 +179,7 @@ final class ChannelHandlerMask {
                     }
                     return false;
                 }
-                return m != null && m.isAnnotationPresent(Skip.class);
+                return m.isAnnotationPresent(Skip.class);
             }
         });
     }