hack: remove list-feature-tests.sh

The script is broken because it relies on grepping the source code.
This has always been fragile (currently it finds the search term
in comments) and stopped working years ago when changing how tests
are labeled.

Instead of fixing the script let's remove it because it's clearly unused.

hack/list-feature-tests.sh

@@ -1,25 +0,0 @@
-#!/usr/bin/env bash
-
-# Copyright 2016 The Kubernetes Authors.
-#
-# 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.
-
-# This script lists all of the [Feature:.+] tests in our e2e suite.
-# Usage: `hack/list-feature-tests.sh`.
-
-set -o errexit
-set -o nounset
-set -o pipefail
-
-KUBE_ROOT=$(dirname "${BASH_SOURCE[0]}")/..
-grep "\[Feature:\w+\]" "${KUBE_ROOT}"/test/e2e/**/*.go -Eoh | LC_ALL=C sort -u