rm .github/workflows for unsupported branch

.github/workflows/pr-build-workflow.yml

@@ -1,22 +0,0 @@
-name: PR Build
-
-on: pull_request
-
-jobs:
-  build:
-    name: Build
-    runs-on: ubuntu-latest
-
-    steps:
-      - uses: actions/checkout@v2
-      - name: Set up JDK
-        uses: actions/setup-java@v1
-        with:
-          java-version: '8'
-      - name: Cache Gradle packages
-        uses: actions/cache@v2
-        with:
-          path: ~/.gradle/caches
-          key: ${{ runner.os }}-gradle-${{ hashFiles('**/*.gradle') }}
-      - name: Build with Gradle
-        run: ./gradlew clean build --continue