Aarch64: remove x86 specifics from os_linux.cpp/hpp/inline.hpp

On aarch64 linux there are the methods "rdtsc" and "supports_sse". These are not called on aarch64, and indeed the rdtsc method tries to emit an rdtsc instruction to store the tsc contents in EAX and EDX, none of which exist on aarch64.

This patch simply cleans them up - they are unused and otherwise cause no harm.