Remove call of ctx.saveChange() from example in plugin documentation

In change I3d8b13 this method was renamed to
ctx.bumpLastUpdatedOn(boolean). Calling it is no longer needed since
the default for bumping the last updated on timestamp was changed to
true by the same change.

Change-Id: Ia8a4dd844fdad077c1173f4707f1bfe86aec4729
Signed-off-by: Edwin Kempin <ekempin@google.com>

Documentation/dev-plugins.txt

@@ -1289,7 +1289,6 @@ public Object apply(RevisionResource rcrs, Input in) {
     bu.addOp(change.getId(), new BatchUpdate.Op() {
       @Override
       public boolean updateChange(BatchUpdate.ChangeContext ctx) {
-        ctx.saveChange();
         return true;
       }
     });