perf util: Remove unused pstack__pop

The last use of pstack__pop() was removed in 2015 by
commit 6422184b087f ("perf hists browser: Simplify zooming code using
pstack_peek()")

Remove it.

Signed-off-by: Dr. David Alan Gilbert <[e-mail]>
Reviewed-by: Ian Rogers <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Namhyung Kim <[e-mail]>

tools/perf/util/pstack.c

···
 	pstack->entries[pstack->top++] = key;
 }
 
-void *pstack__pop(struct pstack *pstack)
-{
-	void *ret;
-
-	if (pstack->top == 0) {
-		pr_err("%s: underflow!\n", __func__);
-		return NULL;
-	}
-
-	ret = pstack->entries[--pstack->top];
-	pstack->entries[pstack->top] = NULL;
-	return ret;
-}
-
 void *pstack__peek(struct pstack *pstack)
 {
 	if (pstack->top == 0)

tools/perf/util/pstack.h

···
 bool pstack__empty(const struct pstack *pstack);
 void pstack__remove(struct pstack *pstack, void *key);
 void pstack__push(struct pstack *pstack, void *key);
-void *pstack__pop(struct pstack *pstack);
 void *pstack__peek(struct pstack *pstack);
 
 #endif /* _PERF_PSTACK_ */