CI: Update to checkout v2, remove install NDK

- Updates to action/checkout v2, which is faster
 - Remove install NDK step, since it's installed by default and speeds up the build

.github/workflows/android.yml

@@ -14,16 +14,13 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-    - uses: actions/checkout@v1
+    - uses: actions/checkout@v2
 
     - name: set up JDK 1.8
       uses: actions/setup-java@v1
       with:
         java-version: 1.8
 
-    - name: Install NDK
-      run: echo "y" | sudo /usr/local/lib/android/sdk/tools/bin/sdkmanager --install "ndk;21.0.6113669" --sdk_root=${ANDROID_SDK_ROOT}
-
     - name: Validate Gradle Wrapper
       uses: gradle/wrapper-validation-action@v1