remove unnecessary build arg

Author: DylanBulmer

.github/workflows/docker-image.yaml

@@ -88,7 +88,6 @@ jobs:
             GIT_COMMIT_TIME=${{ github.event.head_commit.timestamp }}
             GIT_REF=${{ github.ref_name }}
             GIT_WORKFLOW_SHA=${{ github.run_id }}
-            NEXT_PUBLIC_IDP_URL=${{ vars.NEXT_PUBLIC_IDP_URL }}
           cache-from: type=registry,ref=${{ github.ref_name }}
           cache-to: type=inline