Remove unused .html file from shared components

You can import .js files instead of .html files

Change-Id: Ied0c5b00f2915d2a27b54756edf7b37f73b7fc88

polygerrit-ui/app/gr-diff/gr-diff-root.html

@@ -1,18 +0,0 @@
-<!--
-@license
-Copyright (C) 2020 The Android Open Source Project
-
-Licensed under the Apache License, Version 2.0 (the "License");
-you may not use this file except in compliance with the License.
-You may obtain a copy of the License at
-
-http://www.apache.org/licenses/LICENSE-2.0
-
-Unless required by applicable law or agreed to in writing, software
-distributed under the License is distributed on an "AS IS" BASIS,
-WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-See the License for the specific language governing permissions and
-limitations under the License.
--->
-
-<script type="module" src="./gr-diff-root.js"></script>