remove unnecessary synchronized from default decoder (#721)

Signed-off-by: Sergey Tselovalnikov <[email protected]>

Author: SerCeMan

rsocket-core/src/main/java/io/rsocket/frame/decoder/DefaultPayloadDecoder.java

@@ -11,7 +11,7 @@
 class DefaultPayloadDecoder implements PayloadDecoder {
 
   @Override
-  public synchronized Payload apply(ByteBuf byteBuf) {
+  public Payload apply(ByteBuf byteBuf) {
     ByteBuf m;
     ByteBuf d;
     FrameType type = FrameHeaderFlyweight.frameType(byteBuf);