release_delta_base_cache: reuse existing detach function

This function drops an entry entirely from the cache,
meaning that aside from the freeing of the buffer, it is
exactly equivalent to detach_delta_base_cache_entry(). Let's
build on top of the detach function, which shortens the code
and will make it simpler when we change out the underlying
storage in future patches.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

sha1_file.c

@@ -2152,10 +2152,7 @@ static inline void release_delta_base_cache(struct delta_base_cache_entry *ent)
 {
 	if (ent->data) {
 		free(ent->data);
-		ent->data = NULL;
-		ent->lru.next->prev = ent->lru.prev;
-		ent->lru.prev->next = ent->lru.next;
-		delta_base_cached -= ent->size;
+		detach_delta_base_cache_entry(ent);
 	}
 }