Remove unneeded call to EnumChildWindows in nsWindow::BroadcastMsgToChildren, which was causing the system color change message to be dispatched too many times. b=173152 r=dcone sr=kin

widget/src/windows/nsWindow.cpp

@@ -698,8 +698,6 @@ BOOL CALLBACK nsWindow::BroadcastMsgToChildren(HWND aWnd, LPARAM aMsg)
     ::CallWindowProc(winProc, aWnd, aMsg, 0, 0);
 #endif
   }
-  // Send message to children of this window
-  ::EnumChildWindows(aWnd, nsWindow::BroadcastMsgToChildren, aMsg);
   return TRUE;
 }