ci: skip root integration entirely when no root flavor selected

.github/workflows/build.yml

@@ -184,12 +184,6 @@ jobs:
         flavor: ${{ inputs.root_flavor }}
         commit: ${{ inputs.root_commit }}
 
-    - name: Setup KernelSU-Next (legacy)
-      if: ${{ inputs.root_flavor == '' }}
-      uses: ./.github/actions/kernelsu
-      with:
-        ksu_branch: ${{ inputs.ksu_branch }}
-
     - name: Disable SUSFS for ReSukiSU without SUSFS feature
       if: ${{ inputs.root_flavor == 'resukisu' && !contains(inputs.feature_set, 'SUSFS') }}
       uses: ./.github/actions/set-kernel-config