Fix wrong screenId when committing emptyScreens

- Need to increment newScreenId whenever the screen is already bound
- Also cleaned up placeholder on w1 as we now have page pairing logic

Bug: 199160559
Bug: 175939730
Fix: 199131780
Test: drag and drop after clear data
Change-Id: Ic42f3bddfa6cf11b8b726d6181ed2477defde19d