xtensa: drop EXPORT_SYMBOL for common_exception_return

common_exception_return used to be referenced from the oprofile code,
but since oprofile support removal in the commit
a848bf1d ("arch: xtensa: Remove CONFIG_OPROFILE support")
it is no longer supposed to be used by modules.
Drop EXPORT_SYMBOL for common_exception_return.
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

arch/xtensa/kernel/xtensa_ksyms.c

@@ -110,9 +110,6 @@ EXPORT_SYMBOL(__invalidate_icache_range);
 // FIXME EXPORT_SYMBOL(screen_info);
 #endif
 
-extern long common_exception_return;
-EXPORT_SYMBOL(common_exception_return);
-
 #ifdef CONFIG_FUNCTION_TRACER
 EXPORT_SYMBOL(_mcount);
 #endif