dev(ci): use doomemacs/ci commit linter

And move repo-specific linter config into .github/ci.el

.github/workflows/lint-commits.yml

@@ -0,0 +1,5 @@
+name: Lint commits
+on: [push, pull_request]
+jobs:
+  lint-commits:
+    uses: doomemacs/ci/.github/workflows/lint-commits.yml@legacy

.github/workflows/lint.yml

@@ -1,18 +0,0 @@
-name: Commit linter
-on:
-  pull_request:
-jobs:
-  lint-commits:
-    timeout-minutes: 10
-    runs-on: ubuntu-latest
-    steps:
-      - uses: styfle/cancel-workflow-action@0.9.1
-        with:
-          access_token: ${{ github.token }}
-      - uses: purcell/setup-emacs@master
-        with:
-          version: 27.2
-      - uses: actions/checkout@v2.3.1
-        with:
-          fetch-depth: 0
-      - run: bin/doom ci lint-commits ${{ github.event.pull_request.base.sha }} ${{ github.event.pull_request.head.sha }}