Don't ignore reachability of tag objects in fsck

We used to ignore unreachable tags, which just causes problems: it makes
"git prune" leave them around, but since we'll have prune everything
that tag points to, the tag object really should be removed too.

So remove the code that made us think tags were always reachable.

fsck-cache.c

@@ -74,10 +74,6 @@ static void check_connectivity(void)
 			       refs->item->type, sha1_to_hex(refs->item->sha1));
 		}
 
-		/* Don't bother with tag reachability. */
-		if (obj->type == tag_type)
-			continue;
-
 		if (show_unreachable && !(obj->flags & REACHABLE)) {
 			if (obj->attached_deltas)
 				printf("foreign delta reference %s\n",