InputDispatcher_test: Fix death tests

1. All death tests should be in a test suite with a name ending in
   "DeathTest".
2. Silence signal reporting to supress debuggerd stack traces on a
   per-test basis and prevent expected deaths from showing up in system
   stability metrics.

Bug: 212662036
Test: atest inputflinger_tests
Change-Id: Idc070b4c13eea270f76294a3c21f4553363017dc