Remove is_zlib_supported

Remove is_zlib_supported

Since zlib is always supported, there is no need for is_zlib_supported.

binutils/testsuite/

	* binutils-all/compress.exp: Remove is_zlib_supported check.
	* binutils-all/objdump.exp: Likewise.
	* binutils-all/readelf.exp (readelf_compressed_wa_test): Likewise.
	* lib/utils-lib.exp (run_dump_test): Likewise.
	* lib/binutils-common.exp (is_zlib_supported): Removed.

gas/testsuite/

	* lib/gas-defs.exp (run_dump_test): Remove is_zlib_supported check.

ld/testsuite/

	* ld-elf/compress.exp: Remove is_zlib_supported check.
	Fail if --compress-debug-sections doesn't work.
	* lib/ld-lib.exp (run_dump_test): Remove is_zlib_supported check.