util/set: helper to remove entry by key

v2: Add unit test. (Eric Anholt)

Reviewed-by: Eric Anholt <eric@anholt.net>
diff --git a/src/util/set.h b/src/util/set.h
index 4db070a..ffd19a7 100644
--- a/src/util/set.h
+++ b/src/util/set.h
@@ -81,6 +81,8 @@
 
 void
 _mesa_set_remove(struct set *set, struct set_entry *entry);
+void
+_mesa_set_remove_key(struct set *set, const void *key);
 
 struct set_entry *
 _mesa_set_next_entry(const struct set *set, struct set_entry *entry);