Tear down the save dialog and remove it from memory on surface teardown

Otherwise the old save dialog will still be around if the user sets up
another surface (e.g. a second edit), but won't be attached to the DOM.

Bug: 57654
Change-Id: I23c10849a212534bdd0600637d8ad4fa3ebc4fb7
Merge "Tear down the save dialog and remove it from memory on surface teardown"