remove legacy export-build tool support

Signed-off-by: CrazyMax <1951866+crazy-max@users.noreply.github.com>

.github/workflows/ci.yml

@@ -652,35 +652,6 @@ jobs:
         env:
           DOCKER_BUILD_RECORD_RETENTION_DAYS: ${{ matrix.days }}
 
-  export-legacy:
-    runs-on: ubuntu-latest
-    strategy:
-      fail-fast: false
-      matrix:
-        legacy:
-          - false
-          - true
-    steps:
-      -
-        name: Checkout
-        uses: actions/checkout@v6
-      -
-        name: Set up Docker Buildx
-        uses: docker/setup-buildx-action@v3
-        with:
-          version: ${{ inputs.buildx-version || env.BUILDX_VERSION }}
-          driver-opts: |
-            image=${{ inputs.buildkit-image || env.BUILDKIT_IMAGE }}
-      -
-        name: Build
-        uses: ./
-        with:
-          files: |
-            ./test/config.hcl
-          targets: app
-        env:
-          DOCKER_BUILD_EXPORT_LEGACY: ${{ matrix.legacy }}
-
   checks:
     runs-on: ubuntu-latest
     strategy: