This change removes the BlockUntrustedTouchesMode enum, and related
code, as block_untrusted_touches is now always enforced. Removed code and policy to display a toast when an untrusted touch occurs, as it's no longer used.
Fix: 169067926
Test: atest WindowUntrustedTouchTest
Change-Id: I1f8407f523eb845a7c50a2788553bdb2616a394b