Remove `/rebase` GitHub Action since it's no longer necessary

Signed-off-by: Laura Brehm <laurabrehm@hey.com>

.github/workflows/rebase.yml

@@ -1,19 +0,0 @@
-name: Automatic Rebase
-on:
-  issue_comment:
-    types: [created]
-jobs:
-  rebase:
-    name: Rebase
-    if: github.event.issue.pull_request != '' && contains(github.event.comment.body, '/rebase')
-    runs-on: ubuntu-latest
-    steps:
-      - name: Checkout the latest code
-        uses: actions/checkout@v3
-        with:
-          token: ${{ secrets.GITHUB_TOKEN }}
-          fetch-depth: 0 # otherwise, you will fail to push refs to dest repo
-      - name: Automatic Rebase
-        uses: cirrus-actions/rebase@1.4
-        env:
-          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}