perf: Drop guest callback (un)register stubs

Drop perf's stubs for (un)registering guest callbacks now that KVM
registration of callbacks is hidden behind GUEST_PERF_EVENTS=y.  The only
other user is x86 XEN_PV, and x86 unconditionally selects PERF_EVENTS.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Link: https://lore.kernel.org/r/20211111020738.2512932-18-seanjc@google.com

include/linux/perf_event.h

@@ -1511,11 +1511,6 @@ perf_sw_event(u32 event_id, u64 nr, struct pt_regs *regs, u64 addr)	{ }
 static inline void
 perf_bp_event(struct perf_event *event, void *data)			{ }
 
-static inline void perf_register_guest_info_callbacks
-(struct perf_guest_info_callbacks *cbs)					{ }
-static inline void perf_unregister_guest_info_callbacks
-(struct perf_guest_info_callbacks *cbs)					{ }
-
 static inline void perf_event_mmap(struct vm_area_struct *vma)		{ }
 
 typedef int (perf_ksymbol_get_name_f)(char *name, int name_len, void *data);