[llvm-readelf] - Improve ELF type field dumping.
This is related to https://bugs.llvm.org/show_bug.cgi?id=40868.
Currently we don't print OS Specific/`Processor Specific/<unknown>
prefixes when dumping the ELF file type. This is not consistent
with GNU readelf. The patch fixes it.
Also, this patch removes the types.test, because we already have
file-types.test, which tests more cases and this patch revealed that
we have such a duplicate.
Differential revision: https://reviews.llvm.org/D93096