powerpc: Remove export of save_stack_trace_tsk_reliable()

As tglx points out, there are no in-tree module users of
save_stack_trace_tsk_reliable() and its x86 counterpart is not
exported, so remove the powerpc symbol export.
Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Joe Lawrence <joe.lawrence@redhat.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/kernel/stacktrace.c

@@ -220,7 +220,6 @@ int save_stack_trace_tsk_reliable(struct task_struct *tsk,
 
 	return ret;
 }
-EXPORT_SYMBOL_GPL(save_stack_trace_tsk_reliable);
 #endif /* CONFIG_HAVE_RELIABLE_STACKTRACE */
 
 #if defined(CONFIG_PPC_BOOK3S_64) && defined(CONFIG_NMI_IPI)