x86: Remove faulty sanity tests for RTLD build with no multiarch

The sanity tests where meant to ensure that the default implementation
was only being built without multiarch with the exception of the
multiarch/rtld-*.S files.

The code used IS_IN (rtld) to check if the build for was for an
multiarch/rtld-*.S file which is incorrect as IS_IN (rtld) is set for
the non-multiarch build as well.