Optimize Dockerfile and revert to single build platform

.woodpecker/.build_x86.yml

@@ -1,22 +0,0 @@
-labels:
-  platform: linux/amd64
-
-steps:
-  - name: build
-    image: docker
-    when:
-      - branch: master
-        event: push
-    commands:
-      - docker build -t "$REGISTRY_IMAGE_TAG" .
-      - echo "$FORGEJO_REGISTRY_PASSWORD" | docker login "$FORGEJO_REGISTRY_URL" --password-stdin -u "$FORGEJO_REGISTRY_USERNAME"
-      - docker push "$REGISTRY_IMAGE_TAG"
-    volumes:
-      - /var/run/docker.sock:/var/run/docker.sock
-    secrets:
-      [
-        FORGEJO_REGISTRY_URL,
-        FORGEJO_REGISTRY_USERNAME,
-        FORGEJO_REGISTRY_PASSWORD,
-        REGISTRY_IMAGE_TAG,
-      ]