Remove unnecessary environment variable

Author: Wei Sun

.github/workflows/gha_pull_request.yml

@@ -15,7 +15,6 @@ jobs:
     env:
       GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
       DANGER_GITHUB_API_TOKEN: ${{ secrets.DANGER_SWIFT_GITHUB_TOKEN }}
-      LINUX_SOURCEKIT_LIB_PATH: /usr/share/swift/usr/lib
 
   linux:
     runs-on: ubuntu-latest