Revert "Fix WS_Reserve() error handling"

This reverts commit 0e32f166.

 Conflicts:
	bin/varnishd/http2/cache_http2_deliver.c

bin/varnishd/http2/cache_http2_deliver.c

@@ -230,10 +230,8 @@ h2_build_headers(struct vsb *resp, struct req *req)
 	ssize_t sz, sz1;
 
 	l = WS_ReserveAll(req->ws);
-	if (l < 10) {
-		WS_Release(req->ws, 0);
+	if (l < 10)
 		return (-1);
-	}
 
 	AN(VSB_new(resp, req->ws->f, l, VSB_FIXEDLEN));