x86: Remove unused thread_return label from switch_to()

Remove unused thread_return label from switch_to() macro on
x86-64. Since this symbol cuts into schedule(), backtrace at the
latter half of schedule() was always shown as thread_return().

Signed-off-by: Masami Hiramatsu <mhiramat@redhat.com>
Cc: systemtap <systemtap@sources.redhat.com>
Cc: DLE <dle-develop@lists.sourceforge.net>
LKML-Reference: <20091105160359.5181.26225.stgit@harusame>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/include/asm/system.h

@@ -128,8 +128,6 @@ do {									\
 	     "movq %%rsp,%P[threadrsp](%[prev])\n\t" /* save RSP */	  \
 	     "movq %P[threadrsp](%[next]),%%rsp\n\t" /* restore RSP */	  \
 	     "call __switch_to\n\t"					  \
-	     ".globl thread_return\n"					  \
-	     "thread_return:\n\t"					  \
 	     "movq "__percpu_arg([current_task])",%%rsi\n\t"		  \
 	     __switch_canary						  \
 	     "movq %P[thread_info](%%rsi),%%r8\n\t"			  \