Remove unused method (#137)

Author: pzygielo

impl/src/main/java/org/eclipse/parsson/JsonParserImpl.java

@@ -406,10 +406,6 @@ private Context pop() {
             return temp;
         }
 
-        private Context peek() {
-            return head;
-        }
-
         private boolean isEmpty() {
             return head == null;
         }