Remove push-aur job (#4610)

This never built the PR job, and doesn't handle pushing to AUR

The new plan is to have a separate AUR-specific repo that handles events
& rebuilding on dependency-change etc

.github/workflows/push-aur.yml

@@ -1,25 +0,0 @@
----
-name: Build on Arch Linux
-
-on:
-  push:
-    branches:
-      - master
-
-concurrency:
-  group: build-archlinux-${{ github.ref }}
-  cancel-in-progress: true
-
-jobs:
-  build:
-    runs-on: ubuntu-latest
-
-    steps:
-      - name: Sync AUR package with current version
-        uses: pajlada/aur-sync-action@master
-        with:
-          package_name: chatterino2-git
-          commit_username: chatterino2-ci
-          commit_email: chatterino2-ci@pajlada.com
-          ssh_private_key: ${{ secrets.AUR_SSH_PRIVATE_KEY }}
-          dry_run: true