Delete Cosign steps

I don't have the public/private key set up and I kinda want to use the OIDC providers instead anyway.

.github/workflows/build.yaml

@@ -55,19 +55,6 @@ jobs:
           username: ${{ github.actor }}
           password: ${{ secrets.GITHUB_TOKEN }}
 
-      # Sign container
-      - uses: sigstore/[email protected]
-        if: github.event_name != 'pull_request'
-
-      - name: Sign container image
-        if: github.event_name != 'pull_request'
-        run: |
-          cosign sign -y --key env://COSIGN_PRIVATE_KEY ${{ github.actor }}/${{ steps.build_image.outputs.image }}@${TAGS}
-        env:
-          TAGS: ${{ steps.push.outputs.outputs && fromJSON(steps.push.outputs.outputs).digest }}
-          COSIGN_EXPERIMENTAL: false
-          COSIGN_PRIVATE_KEY: ${{ secrets.SIGNING_SECRET }}
-
       - name: Echo outputs
         if: github.event_name != 'pull_request'
         run: |