Android CI: Configure with CMAKE_ANDROID_API (#6284)

CMAKE_ANDROID_API will set CMAKE_SYSTEM_VERSION if it's not defined.

Also remove setting CMake variable values that don't affect the ability
to successfully configure in CI.

.github/workflows/android-build.yml

@@ -27,7 +27,7 @@ jobs:
       run:  |
         mkdir build
         cd build
-        cmake -DCMAKE_BUILD_TYPE=${{ env.BUILD_TYPE }} -DCMAKE_SYSTEM_NAME=Android -DCMAKE_SYSTEM_VERSION=21 -DCMAKE_ANDROID_ARCH_ABI=${{ matrix.android-abi }} "-DCMAKE_ANDROID_NDK=$ANDROID_NDK_LATEST_HOME" -DZ3_BUILD_JAVA_BINDINGS=TRUE -G "Unix Makefiles" -DJAVA_AWT_LIBRARY=NotNeeded -DJAVA_JVM_LIBRARY=NotNeeded -DJAVA_INCLUDE_PATH2=NotNeeded -DJAVA_AWT_INCLUDE_PATH=NotNeeded ../
+        cmake -DCMAKE_BUILD_TYPE=${{ env.BUILD_TYPE }} -DCMAKE_SYSTEM_NAME=Android -DCMAKE_ANDROID_API=21 -DCMAKE_ANDROID_ARCH_ABI=${{ matrix.android-abi }} "-DCMAKE_ANDROID_NDK=$ANDROID_NDK_LATEST_HOME" -DZ3_BUILD_JAVA_BINDINGS=TRUE -G "Unix Makefiles" ../
         make -j $(nproc)
         tar -cvf z3-build-${{ matrix.android-abi }}.tar *.jar *.so