SurfaceTextureHelper: Remove use of quitSafely() because it's API lvl 18

There is no reason to not just quit() in release().

Review URL: https://codereview.webrtc.org/1418563005

Cr-Commit-Position: refs/heads/master@{#10394}

talk/app/webrtc/java/android/org/webrtc/SurfaceTextureHelper.java

@@ -223,7 +223,7 @@ final class SurfaceTextureHelper {
     surfaceTexture.release();
     eglBase.release();
     if (isOwningThread) {
-      handler.getLooper().quitSafely();
+      handler.getLooper().quit();
     }
   }
 }