x86/boot: Remove unused copy_*_gs() functions

copy_from_gs() and copy_to_gs() are unused in the boot code. They have
actually never been used -- they were always commented out since their
addition in 2007:

  5be86566 ("String-handling functions for the new x86 setup code.")

So remove them -- they can be restored from history if needed.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20170531081243.5709-1-jslaby@suse.cz


Signed-off-by: Ingo Molnar <mingo@kernel.org>