selftests/x86/pkeys: Remove unused functions

This also gets rid of two build warnings:

  protection_keys.c: In function ‘dumpit’:
  protection_keys.c:419:3: warning: ignoring return value of ‘write’, declared with attribute warn_unused_result [-Wunused-result]
     write(1, buf, nr_read);
     ^~~~~~~~~~~~~~~~~~~~~~

Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Shuah Khan <shuahkh@osg.samsung.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>