Remove dead firebase key reference (#1467)

.gitallowed

@@ -1,6 +0,0 @@
-# Part of the Carbon Language project, under the Apache License v2.0 with LLVM
-# Exceptions. See /LICENSE for license information.
-# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-
-# Firebase API key
-AIzaSyDyAAcQeReDNXVUd_ZdkSzYgqIDJe-kPK8