Removed samply/directory-sync part of the GitHub build

Since the directory-sync repo has been absorbed into
directory_sync_service, we don't need to import and build its code
any more.

.github/workflows/ci.yml

@@ -17,18 +17,6 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-    - name: Clone directory-sync repository
-      uses: actions/checkout@v2
-      with:
-        repository: samply/directory-sync
-        path: directory-sync
-        ref: master
-
-    - name: Build directory-sync library
-      run: |
-        cd directory-sync
-        mvn clean install
-
     - name: Check out Git repository
       uses: actions/checkout@v3