remove unused Swift 6 language mode workflow (#130)

remove unused Swift 6 language mode workflow

Author: rnro

.github/workflows/pull_request.yml

@@ -28,8 +28,3 @@ jobs:
       name: "Integration test"
       matrix_linux_command: "apt-get update -yq && apt-get install -yq jq && ./scripts/run-integration-test.sh"
       matrix_linux_nightly_main_enabled: false
-
-  swift-6-language-mode:
-    name: Swift 6 Language Mode
-    uses: apple/swift-nio/.github/workflows/swift_6_language_mode.yml@main
-    if: false  # Disabled for now.