selftests: futex: delete RUN_TESTS and EMIT_TESTS overrides

Delete RUN_TESTS and EMIT_TESTS overrides and use common defines in
lib.mk. Common defines work just fine and there is no need to define
custom overrides.

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>