Now that run_tests.sh has been cleaned up to remove (or move) test
groups that weren't very useful, remove the concept of test groups and
just run all the tests.
The reason that run_tests.sh supported running checksum_benchmarks.sh is
that as a side effect, checksum_benchmarks.sh runs the 'test_checksums'
program with all combinations of CPU features.
However, commit ec60cb48d11c ("tools/run_tests.sh: test different
combinations of CPU features") made run_tests.sh handle this elsewhere.
So having run_tests.sh run checksum_benchmarks.sh is no longer useful.
Keep checksum_benchmarks.sh around for manual benchmark runs, however.
android_tests is only useful for local testing, and it wasn't being run
in Travis CI. Move it into a separate script to avoid complicating
run_tests.sh.
This was only useful for me to do local testing, I don't have the needed
MIPS router available anymore, and its main purpose was test a big
endian system but that's now covered by testing s390x with Travis CI.
