Fixed unnecessary layouting on wifi signal changes

This could cause a layout every few hundred ms, even
when the QS panel was closed.

Bug: 17001532
Change-Id: I3f2b9b9621dced7f5b6fff67d24efc7444b0a9ad

packages/SystemUI/src/com/android/systemui/qs/SignalTileView.java

@@ -89,11 +89,9 @@ public final class SignalTileView extends QSTileView {
     protected void handleStateChanged(QSTile.State state) {
         super.handleStateChanged(state);
         final SignalState s = (SignalState) state;
-        mSignal.setImageDrawable(null);  // force refresh
         mSignal.setImageResource(s.iconId);
         if (s.overlayIconId > 0) {
             mOverlay.setVisibility(VISIBLE);
-            mOverlay.setImageDrawable(null);  // force refresh
             mOverlay.setImageResource(s.overlayIconId);
         } else {
             mOverlay.setVisibility(GONE);