perf: Remove unused extern declaration arch_perf_get_page_size()

commit 8af26be ("perf/core: Fix arch_perf_get_page_size()")
left behind this.

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20230725135038.25060-1-yuehaibing@huawei.com

Author: YueHaibing

include/linux/perf_event.h

@@ -1860,10 +1860,6 @@ extern void arch_perf_update_userpage(struct perf_event *event,
 				      struct perf_event_mmap_page *userpg,
 				      u64 now);
 
-#ifdef CONFIG_MMU
-extern __weak u64 arch_perf_get_page_size(struct mm_struct *mm, unsigned long addr);
-#endif
-
 /*
  * Snapshot branch stack on software events.
  *