Removed regionId from updateTapExcludeRegion request.

There was no need for regionId in the request since you can just replace
the previous region with a new one. This reduces confusion and
simplifies the code. This also allowed TapExcludeRegionHolder to get
deleted and just store the excluded region in the WindowState.

Additionally, this fixed a bug where the excluded region would get
overwritten when the window region was smaller. If the window region was
resized later, the exclude region would remain small.

This is also preparing for more uses of this API with embedded windows
and window magnification.

Test: ActivityViewTest
Change-Id: Ia151115b5a5e8f2ce5e606fe627821dcfef5d9b5