usctest.h: Cleanup.

Signed-off-by: Cyril Hrubis <chrubis@suse.cz>
usctest.h: Remove dumbious _USC_LIB_ ifdefs.

This is overcomplicated without a reason and causes build failures due
to missing symbols on uClinux.

Also remove all _USC_LIB_ defines and referencies.

Reported-by: Benoit Marcot <Benoit.Marcot@arm.com>
Signed-off-by: Cyril Hrubis <chrubis@suse.cz>