[llvm-readobj] - Refine program headers testing (`-l`, `--program-headers` and `--segment`).

We have `gnu-phdrs.test` that tests
`-l`, `--program-headers` and `--segment` options for `llvm-readelf`.

We also have:
1) `program-headers.test` that tests `--program-headers` and `-l`
   for `llvm-readobj`. It doesn't test `--segment` and also uses
   lots of precompiled objects. It is very incomplete in compare
   with the `gnu-phdrs.test`.

2) `pt-gnu-property.test` that contains a simple test for the
   `PT_GNU_PROPERTY` segment. There is no reason to have it in
   a separate file.

This patch:
1) Merges `program-headers.test` and `pt-gnu-property.test` to `gnu-phdrs.test`.
2) Removes 2 precompiled binaries used by `program-headers.test`
   (other ones are still used by another tests).

Differential revision: https://reviews.llvm.org/D85526