android: Install the libmpd.so output on android

libmpd.so was getting written as a file called `arm64-v8a` instead of `arm64-v8a/libmpd.so`

android/apk/meson.build

@@ -1,13 +0,0 @@
-android_abi = get_option('android_abi')
-
-mpd_so = custom_target(
-  'libmpd.so',
-  output: 'libmpd.so',
-  input: mpd,
-  command: [
-    'cp',
-    '@INPUT@',
-    join_paths(meson.current_source_dir(), '../app/src/main/jnilibs/', android_abi),
-  ],
-  build_by_default: true
-)

android/build.py

@@ -68,3 +68,5 @@ run_meson(toolchain, mpd_path, '.', configure_args)
 
 ninja = shutil.which("ninja")
 subprocess.check_call([ninja], env=toolchain.env)
+
+subprocess.check_call([ninja, 'install'], env=toolchain.env)