Bug 1354900 - Remove ASSERT when plugin incorrectly finalizes async surface. r=dvander

Flash currently has a bug that trips an ASSERT in debug builds when async painting incorrectly finalizes the currently active surface.  This is related to their fix for bug 1306698.  We are removing this assertion so that plugin work can proceed with debug builds.

dom/plugins/ipc/PluginInstanceChild.cpp

@@ -2909,10 +2909,6 @@ PluginInstanceChild::NPN_FinalizeAsyncSurface(NPAsyncSurface *surface)
         return NPERR_GENERIC_ERROR;
     }
 
-    // The API forbids this. If it becomes a problem we can revoke the current
-    // surface instead.
-    MOZ_ASSERT(!surface || mCurrentDirectSurface != surface);
-
     switch (mDrawingModel) {
     case NPDrawingModelAsyncBitmapSurface: {
         RefPtr<DirectBitmap> bitmap;