CI: Drop unneeded cargo-ndk tool from build-test (#476)

A recent borked `cargo-ndk` release [^1] [^2] lead me to investigate
why we are using a nonstandard tool in our CI in the first place.
Compiling / build-testing the `ndk` crate does not require any external
tooling whatsoever nor an SDK setup: this crate is a pure wrapper over
pre-generated C bindings in the `ndk-sys` crate, which only require
NDK _libraries_ (and an Android-capable linker) when linking actual
runnable binaries (typically shared libraries or executables).  And the
Rust compiler natively supports compiling Rust code for Android targets.

[^1]: https://github.com/rust-mobile/ndk/actions/runs/9149848316
[^2]: https://togithub.com/bbqsrc/cargo-ndk/pull/135#discussion_r1606097922

.github/workflows/rust.yml

@@ -70,38 +70,32 @@ jobs:
         os: [ubuntu-latest]
         rust-channel: [stable, nightly]
         rust-target:
-          - { triple: "armv7-linux-androideabi", abi: armeabi-v7a }
-          - { triple: "aarch64-linux-android", abi: arm64-v8a }
-          - { triple: "i686-linux-android", abi: x86 }
-          - { triple: "x86_64-linux-android", abi: x86_64 }
+          - armv7-linux-androideabi
+          - aarch64-linux-android
+          - i686-linux-android
+          - x86_64-linux-android
         include:
           - os: windows-latest
             rust-channel: stable
-            rust-target: { triple: "aarch64-linux-android", abi: arm64-v8a }
+            rust-target: aarch64-linux-android
           - os: windows-latest
             rust-channel: stable
-            rust-target: { triple: "x86_64-linux-android", abi: x86_64 }
+            rust-target: x86_64-linux-android
 
     runs-on: ${{ matrix.os }}
     name: Cross-compile
 
     steps:
       - uses: actions/checkout@v4
 
-      - name: Setup Android SDK
-        uses: android-actions/setup-android@v2
-
-      - name: Install cargo-ndk
-        run: cargo install cargo-ndk
-
-      - name: Installing Rust ${{ matrix.rust-channel }} w/ ${{ matrix.rust-target.triple }}
+      - name: Installing Rust ${{ matrix.rust-channel }} w/ ${{ matrix.rust-target }}
         uses: dtolnay/rust-toolchain@master
         with:
-          target: ${{ matrix.rust-target.triple }}
+          target: ${{ matrix.rust-target }}
           toolchain: ${{ matrix.rust-channel }}
 
-      - name: Compile for ${{ matrix.rust-target.triple }}
-        run: cargo ndk -t ${{ matrix.rust-target.abi }} build
+      - name: Compile for ${{ matrix.rust-target }}
+        run: cargo build --target ${{ matrix.rust-target }}
 
   build-host:
     strategy: