Remove public usages of FLAG_BLUR_BEHIND

WindowManager.LayoutParams.FLAG_BLUR_BEHIND has been deprecated since
2011 and has been a no-op ever since.
We are @remove-ing it in S and making it a SystemApi to be used for
cross-app blurs. To that end, we have to remove its public usages.

This CL removes its usage in ApiDemos.

Bug: 177524486
Test: m
Change-Id: I3683db296e8331a9d255d39f23fad7dedc28bb9b
4 files changed