.github/workflows: remove one-off darwin/amd64 backfill workflow

Updates #676

.github/workflows/darwin-amd64-backfill.yml

@@ -1,51 +0,0 @@
-name: Backfill darwin/amd64 binaries for v1.3.0 and v1.3.1
-
-on:
-  workflow_dispatch:
-
-permissions:
-  contents: write
-  attestations: write
-  id-token: write
-
-jobs:
-  build:
-    name: Build darwin/amd64 for ${{ matrix.version }}
-    runs-on: ubuntu-latest
-    strategy:
-      matrix:
-        version: [v1.3.0, v1.3.1]
-    steps:
-      - name: Checkout repository at ${{ matrix.version }}
-        uses: actions/checkout@v5
-        with:
-          ref: ${{ matrix.version }}
-          fetch-depth: 0
-          persist-credentials: false
-      - name: Install Go
-        uses: actions/setup-go@v6
-        with:
-          go-version-file: go.mod
-          cache: false
-      - name: Build binary
-        run: |
-          VERSION="${{ matrix.version }}"
-          DIR="$(mktemp -d)"
-          mkdir "$DIR/age"
-          go build -o "$DIR/age" -trimpath ./cmd/...
-          cp LICENSE "$DIR/age/LICENSE"
-          cat .github/workflows/LICENSE.suffix.txt >> "$DIR/age/LICENSE"
-          tar -cvzf "age-$VERSION-darwin-amd64.tar.gz" -C "$DIR" age
-        env:
-          CGO_ENABLED: 0
-          GOOS: darwin
-          GOARCH: amd64
-      - name: Generate artifact attestation
-        uses: actions/attest-build-provenance@v3
-        with:
-          subject-path: age-${{ matrix.version }}-darwin-amd64.tar.gz
-      - name: Upload to release
-        run: gh release upload "${{ matrix.version }}" "age-${{ matrix.version }}-darwin-amd64.tar.gz"
-        env:
-          GH_REPO: ${{ github.repository }}
-          GH_TOKEN: ${{ github.token }}