[github-actions] remove android-ndk platform and CI job (#12654)

This commit removes the `android-ndk` platform support from the
`script/cmake-build` script and deletes the associated CI job from
the GitHub Actions workflow.

The `android-ndk` build was used to verify OpenThread compatibility
with the Android NDK. However, since OpenThread is now officially
included in the Android platform, maintaining a separate NDK-based
build in this repository is no longer necessary.

Changes:
- Remove `android-ndk` from `OT_PLATFORMS` in `script/cmake-build`.
- Remove NDK-specific configuration logic in `script/cmake-build`.
- Remove the `android-ndk` job from `.github/workflows/build.yml`.

script/cmake-build

@@ -67,7 +67,7 @@ OT_CMAKE_NINJA_TARGET=${OT_CMAKE_NINJA_TARGET-}
 OT_SRCDIR="$(cd "$(dirname "$0")"/.. && pwd)"
 readonly OT_SRCDIR
 
-OT_PLATFORMS=(simulation posix android-ndk)
+OT_PLATFORMS=(simulation posix)
 readonly OT_PLATFORMS
 
 OT_CLEAN_INTERMEDIATES="${OT_CLEAN_INTERMEDIATES-${GITHUB_ACTION-}}"
@@ -166,58 +166,6 @@ main()
     )
 
     case "${platform}" in
-        android-ndk)
-            if [ -z "${NDK-}" ]; then
-                echo "
-The 'NDK' environment variable needs to point to the Android NDK toolchain.
-Please ensure the NDK is downloaded and extracted then try to run this script again
-
-For example:
-    NDK=/opt/android-ndk-r25c ./script/cmake-build-android
-
-You can download the NDK at https://developer.android.com/ndk/downloads
-
-            "
-                exit 1
-            fi
-
-            NDK_CMAKE_TOOLCHAIN_FILE="${NDK?}/build/cmake/android.toolchain.cmake"
-            if [ ! -f "${NDK_CMAKE_TOOLCHAIN_FILE}" ]; then
-                echo "
-Could not fild the Android NDK CMake toolchain file
-- NDK=${NDK}
-- NDK_CMAKE_TOOLCHAIN_FILE=${NDK_CMAKE_TOOLCHAIN_FILE}
-
-            "
-                exit 2
-            fi
-            local_options+=(
-                "-DOT_LOG_OUTPUT=PLATFORM_DEFINED"
-
-                # Add Android NDK flags
-                "-DOT_ANDROID_NDK=1"
-                "-DCMAKE_TOOLCHAIN_FILE=${NDK?}/build/cmake/android.toolchain.cmake"
-
-                # Android API needs to be >= android-24 for `getifsaddrs()`
-                "-DANDROID_PLATFORM=android-24"
-
-                # Store thread settings in the CWD when executing ot-cli or ot-daemon
-                '-DOT_POSIX_SETTINGS_PATH="./thread"'
-            )
-
-            # Rewrite platform to posix
-            platform="posix"
-
-            # Check if OT_DAEMON or OT_APP_CLI flags are needed
-            if [[ ${OT_CMAKE_NINJA_TARGET[*]} =~ "ot-daemon" ]] || [[ ${OT_CMAKE_NINJA_TARGET[*]} =~ "ot-ctl" ]]; then
-                local_options+=("-DOT_DAEMON=ON")
-            elif [[ ${OT_CMAKE_NINJA_TARGET[*]} =~ "ot-cli" ]]; then
-                local_options+=("-DOT_APP_CLI=ON")
-            fi
-
-            options+=("${local_options[@]}")
-            ;;
-
         posix)
             local_options+=(
                 "-DOT_TCP=OFF"