Remove unused xmllint-html.sh script

There are no longer any HTML files in the BIND 9 source repository.
Remove the xmllint-html.sh script that was used in the past to check
those for errors.

.gitlab-ci.yml

@@ -619,7 +619,6 @@ misc:
     - sh util/check-gitignore.sh
     - sh util/check-trailing-whitespace.sh
     - bash util/unused-headers.sh
-    - bash util/xmllint-html.sh
     # Check dangling symlinks in the repository
     - if find . -xtype l | grep .; then exit 1; fi
     - muon-meson analyze -Werror

util/xmllint-html.sh

@@ -1,22 +0,0 @@
-#!/bin/sh -f
-
-# Copyright (C) Internet Systems Consortium, Inc. ("ISC")
-#
-# SPDX-License-Identifier: MPL-2.0
-#
-# This Source Code Form is subject to the terms of the Mozilla Public
-# License, v. 2.0.  If a copy of the MPL was not distributed with this
-# file, you can obtain one at https://mozilla.org/MPL/2.0/.
-#
-# See the COPYRIGHT file distributed with this work for additional
-# information regarding copyright ownership.
-
-files=$(git ls-files '*.html')
-if test -n "$files"; then
-  xmllint --noout --nonet --html $files 2>&1 \
-    | awk 'BEGIN { status = 0; }
-	     # suppress HTML 5 <section> tag errors
-	     /HTML parser error : Tag section invalid/ { getline; getline; next; }
-	     { print; status = 1; }
-	     END { exit status }'
-fi