x86_64: cleanup tsc.c merge artifact

tsc_unstable is declared twice.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/x86_64/kernel/tsc.c

@@ -118,8 +118,6 @@ core_initcall(cpufreq_tsc);
 
 #endif
 
-static int tsc_unstable = 0;
-
 /*
  * Make an educated guess if the TSC is trustworthy and synchronized
  * over all CPUs.