Remove build variant "tests"

Bug: 5368571
Now we have a phony target "tests" instead.
The target can be built in any other build variant (eg userdebug).
For example, "make PRODUCT-full-userdebug tests dist" will build and
put the *-test-* zip file in the dist dir.
The "tests" target will include all modules tagged as "tests" in
addition to other modules in specific target out directories.

Change-Id: I8383097380d8e6846c3e2107d6dd5f68788cfc39
4 files changed