Release input surface of drag completely

Once the input surface needs to be hidden, it never shows
again, so the surface can be removed when the drag is done.

Bug: 138656611
Test: atest DragDropControllerTests
Test: After a drag and drop operation is done, there won't
      have lots of error log when constantly touching screen:
      "Window handle drag has no registered input channel".
      And the CloseGuard of the input surface won't complain
      when finalizing.

Change-Id: I262867c118aeb1a6d091132fac15056dee5fa3f1