Remove legacy-test and legacy-android-test targets

Fixes up the android.test.legacy target to stop using sources directly
now that the issue with android.test.runner-minus-junit not being able
to be built against the SDK has been resolved.

Also, fixes a couple of comments.

Bug: 63127064
Test: make checkbuild
Change-Id: If38fa0d87b36343896e97efb2269ac070810db84