8285745: Re-examine PushbackInputStream mark/reset

Reviewed-by: jpai, alanb

src/java.base/share/classes/java/io/PushbackInputStream.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1994, 2021, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1994, 2022, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -345,7 +345,7 @@ public boolean markSupported() {
      *                      the mark position becomes invalid.
      * @see     java.io.InputStream#reset()
      */
-    public synchronized void mark(int readlimit) {
+    public void mark(int readlimit) {
     }
 
     /**
@@ -360,7 +360,7 @@ public synchronized void mark(int readlimit) {
      * @see     java.io.InputStream#mark(int)
      * @see     java.io.IOException
      */
-    public synchronized void reset() throws IOException {
+    public void reset() throws IOException {
         throw new IOException("mark/reset not supported");
     }