[MC] Remove unneeded zlib opt-out for .debug_frame

The opt-out from rL236267 (2015) is untested and seems no longer needed (or not
needed when rL236267 was committed): there is nothing special with uncompressed
alignment. This brings us in line with GCC which compresses .debug_frame .

Checked that -g -fno-asynchronous-unwind-tables + objcopy
--decompress-debug-sections output is identical to -g
-fno-asynchronous-unwind-tables -gz + objcopy --decompress-debug-sections
output.