Use the latest version of the Android NDK

.github/workflows/test-android.yaml

@@ -9,22 +9,10 @@ on:
       - "bdk-ffi/**"
       - "bdk-android/**"
 
-env:
-  ANDROID_NDK_ROOT: /usr/local/lib/android/sdk/ndk/21.4.7075529
-  # By default, the new ubuntu-20.04 images use the following ANDROID_NDK_ROOT
-  # ANDROID_NDK_ROOT: /usr/local/lib/android/sdk/ndk/25.0.8775105
-
 jobs:
   build:
     runs-on: ubuntu-20.04
     steps:
-      - name: "Install Android NDK 21.4.7075529"
-        run: |
-          ANDROID_ROOT=/usr/local/lib/android
-          ANDROID_SDK_ROOT=${ANDROID_ROOT}/sdk
-          SDKMANAGER=${ANDROID_SDK_ROOT}/cmdline-tools/latest/bin/sdkmanager
-          echo "y" | $SDKMANAGER "ndk;21.4.7075529"
-
       - name: "Check out PR branch"
         uses: actions/checkout@v2