Remove unnecessary filtering of android.test.mock files

Previously the android.test.mock files were in the test-runner/src
directory so had to be filtered out of the android.test.runner source
files but the android.test.mock files are now in their own test-mock/src
directory so the filtering is no longer required.

Bug: 30188076
Test: make checkbuild
Change-Id: I1f28fc0735e16fa166663e5797af641b08a4926c