Fix unused and deprecation warnings

Despite our best efforts to resolve warnings, some new ones slipped in
late this afternoon.

Change-Id: I4b8f8bba08de2d5c7a2a03c04d121c0e447bfa8e
Signed-off-by: Shawn O. Pearce <sop@google.com>

gerrit-gwtui/src/main/java/com/google/gerrit/client/patches/PatchScreen.java

@@ -112,9 +112,6 @@ public abstract class PatchScreen extends Screen implements
         }
       };
 
-  // The change id for which the above patch set id's are valid
-  private static Change.Id currentChangeId = null;
-
   protected final Patch.Key patchKey;
   protected PatchSetDetail patchSetDetail;
   protected PatchTable fileList;