x86/tsc: Remove the unused check_tsc_disabled()

check_tsc_disabled() was introduced by commit:

  c73deb6a ("perf/x86: Add ability to calculate TSC from perf sample timestamps")

The only caller was arch_perf_update_userpage(), which had been refactored
by commit:

  d8b11a0c

 ("perf/x86: Clean up cap_user_time* setting")

... so no need keep and export it any more.

Signed-off-by: Wei Jiangang <weijg.fnst@cn.fujitsu.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: a.p.zijlstra@chello.nl
Cc: adrian.hunter@intel.com
Cc: bp@suse.de
Link: http://lkml.kernel.org/r/1468570330-25810-1-git-send-email-weijg.fnst@cn.fujitsu.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>