DEV: Remove the scheduled ember plugins workflow (#17011)

It hasn't worked once in 9 months 😉 and ember cli plugin tests are now a part of the main workflow (since 8a69de7964)

.github/workflows/ember_with_plugins.yml

@@ -1,49 +0,0 @@
-name: (experimental) Ember CLI tests (plugins)
-
-on:
-  schedule:
-    - cron: "0 0 * * *"
-
-jobs:
-  build:
-    name: run
-    runs-on: ubuntu-latest
-    container: discourse/discourse_test:slim-browsers
-    timeout-minutes: 60
-
-    steps:
-      - uses: actions/checkout@v3
-        with:
-          fetch-depth: 1
-
-      - name: Setup Git
-        run: |
-          git config --global user.email "ci@ci.invalid"
-          git config --global user.name "Discourse CI"
-
-      - name: Get yarn cache directory
-        id: yarn-cache-dir
-        run: echo "::set-output name=dir::$(yarn cache dir)"
-
-      - name: Yarn cache
-        uses: actions/cache@v3
-        id: yarn-cache
-        with:
-          path: ${{ steps.yarn-cache-dir.outputs.dir }}
-          key: ${{ runner.os }}-yarn-${{ hashFiles('**/yarn.lock') }}
-          restore-keys: |
-            ${{ runner.os }}-yarn-
-
-      - name: Official Plugins Install
-        run: |
-          bundle config --local path vendor/bundle
-          bundle config --local deployment true
-          bundle config --local without development
-          bundle install --jobs 4
-          bundle clean
-          bundle exec rake plugin:install_all_official
-
-      - name: QUnit
-        working-directory: ./app/assets/javascripts/discourse
-        run: QUNIT_EMBER_CLI=1 sudo -E -u discourse -H rake plugin:qunit
-        timeout-minutes: 60