We don't need this action anymore.

Jenkins builds all local branches whilst GitHub Actions builds all PRs.

.github/workflows/maven.yml

@@ -1,17 +0,0 @@
-name: Java CI
-
-on: [push, pull_request]
-
-jobs:
-  build:
-
-    runs-on: ubuntu-latest
-
-    steps:
-    - uses: actions/checkout@v1
-    - name: Set up JDK 1.8
-      uses: actions/setup-java@v1
-      with:
-        java-version: 1.8
-    - name: Build with Maven
-      run: mvn -B package --file pom.xml