perf/core: Drop prototype for defunct arch_perf_get_page_size()

arch_perf_get_page_size() was removed in 5.11, so this removal of
the useless prototype is long overdue.

Signed-off-by: Marc Zyngier <maz@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Mark Rutland <mark.rutland@arm.com>

include/linux/perf_event.h

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index c8dcfdb..0dcb8b3 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -1849,10 +1849,6 @@ 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.
  *