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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