selftests: mqueue: delete RUN_TESTS and EMIT_TESTS overrides

Delete RUN_TESTS and EMIT_TESTS overrides and use common defines in lib.mk.
The overrides are in place to call mq_open_tests with queue name argument.
The change to delete overrides is coupled with a change to mq_open_tests
to use default queue name when it is called without one.

Signed-off-by: Shuah Khan (Samsung OSG) <shuah@kernel.org>
Reviewed-by: Anders Roxell <anders.roxell@linaro.org>
Signed-off-by: Shuah Khan (Samsung OSG) <shuah@kernel.org>