Revert "workflow: build ARM64 image alongside amd64"

This doesn't work, because we need some of devkitPro's tools. And
devkitPro doesn't compile for ARM... last I checked.

This reverts commit 165af33.

.github/workflows/main.yml

@@ -10,13 +10,9 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
-      - name: Set up QEMU
-        uses: docker/setup-qemu-action@v3
-      - name: Set up Docker Buildx
-        uses: docker/setup-buildx-action@v3
+        uses: actions/checkout@v3
       - name: Set up Python 3.11
-        uses: actions/setup-python@v5
+        uses: actions/setup-python@v4
         with:
           python-version: 3.11
       - name: Install testing dependencies
@@ -37,7 +33,7 @@ jobs:
         with:
           context: .
           file: ./Dockerfile
-          platforms: linux/amd64,linux/arm64
+          platforms: linux/amd64
           push: true
           tags: ghcr.io/ds-homebrew/twlhelper:latest
       - name: Reboot TWLHelper