chore(ci): Drop kernel signer, this is handled in the ublue kernel ca…

…che now.

.github/workflows/build.yml

@@ -256,15 +256,6 @@ jobs:
           extra-args: |
             --target=${{ matrix.base_name }}
 
-      - name: Sign kernel
-        uses: ublue-os/[email protected]
-        with:
-          image: ${{ steps.build_image.outputs.image }}
-          default-tag: ${{ env.DEFAULT_TAG }}
-          privkey: ${{ secrets.AKMOD_PRIVKEY_20230518 }}
-          pubkey: /etc/pki/akmods/certs/akmods-ublue.der
-          tags: ${{ steps.build_image.outputs.tags }}
-
       # Workaround bug where capital letters in your GitHub username make it impossible to push to GHCR.
       # https://github.com/macbre/push-to-ghcr/issues/12
       - name: Lowercase Registry