Remove the unused CI job (#7853)

---

Fixes #7754

This CI job already be removed. And the check require is removed. So let's
remove this file.

.github/workflows/ci-unit-flaky.yaml

-#
-# Licensed to the Apache Software Foundation (ASF) under one
-# or more contributor license agreements.  See the NOTICE file
-# distributed with this work for additional information
-# regarding copyright ownership.  The ASF licenses this file
-# to you 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 dummy github workflow is needed since github is configured to have this
-# job pass as a checkin requirement. Once that restriction is moved it's safe
-# to delete this file.
-
-name: CI - Unit - Flaky
-on:
-  pull_request:
-    branches:
-      - master
-  push:
-    branches:
-      - branch-*
-
-jobs:
-
-  unit-test-flaky:
-    name:
-    runs-on: ubuntu-latest
-    timeout-minutes: 120
-
-    steps:
-      - name: checkout
-        uses: actions/checkout@v2
-        with:
-          fetch-depth: 0
-          ref: ${{ github.event.pull_request.head.sha }}