Fix memory leak of Dnd tile

The instance of Dnd tile leaks when user taps the edit button
of Quick Settings. To fix this issue, QSTile#destroy should be
called when the tile is no longer needed.

Bug: 32103239
Test: manual - go to Quick Settings -> Edit repeatedly

Change-Id: I9bc9ee836be5c8e46eb1ccd202bd5cc50070ef47