Don't emit tests in AndroidMkForFiles

I'm moving the installation of test files to soong. Marking a make
module as a test will make Make start expecting more soong-built test
files. But the apex rules won't generate these files for their
pseudo-modules representing files inside the apex. So instead, just make
those modules not tests.

Bug: 388850000
Test: Presubmits
Change-Id: I9c7d3980beac8d7ad2d758ba99e8ec6895c25f06