Android uninstall 31 (#2533)

# Objective

- Related to #2514 - not sure if it's a proper fix long term
- CI was complaining Error: Path `"/usr/local/lib/android/sdk/ndk-bundle/toolchains/llvm/prebuilt/linux-x86_64/bin/aarch64-linux-android31-clang"` was not found
- A lot of questions started popping up 10 days ago about ["android build tools 31 corrupted"](https://www.google.com/search?q=android+build+tools+31+corrupted)
  - https://stackoverflow.com/questions/68387270/android-studio-error-installed-build-tools-revision-31-0-0-is-corrupted
- Uninstalling `"build-tools;31.0.0"` doesn't seem to work, as it removes other components even though `"build-tools;30.0.3"` are available


## Solution

- Uninstalling `"platforms;android-31"` seems to do the trick and `cargo-apk` stops trying to target `...31`

Android is not my thing, this solution was found with a lot of trials and errors. I am not sure how long term it is, I don't know the release schedule of android build tools, or if we need to target this 31 thing. I just wanted to stop all those failed ci everywhere...

.github/bors.toml

@@ -5,6 +5,7 @@ status = [
     "build (nightly, ubuntu-latest)",
     "build-wasm (stable, ubuntu-latest)",
     "build-wasm (nightly, ubuntu-latest)",
+    "build-android",
     "markdownlint",
     "check-markdown-links",
     "run-examples",

.github/workflows/ci.yml

@@ -71,6 +71,8 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v2
+      - name: Uninstall android-31
+        run: $ANDROID_SDK_ROOT/cmdline-tools/latest/bin/sdkmanager --uninstall "platforms;android-31"
       - name: Install Android targets
         run: rustup target add aarch64-linux-android armv7-linux-androideabi
       - name: Install Cargo APK