[llvm-readobj][test] - Add a test for testing regular section flags and cleanup flags testing.

This:
1) Adds a test for testing all section flags (`section-flags.test`).
2) Renames `sec-flags.test`->`section-arch-flags.test`
   and performs a clean up.
3) Removes `compression.zlib.style.elf-x86-64` binary and a test case
   for SHF_COMPRESSED flag, because them are now excessive.
4) Adds missing MIPS flags and a test for SHF_ARM_PURECODE.

Differential revision: https://reviews.llvm.org/D71333