- PostIt.Android.csproj: drop Xamarin.AndroidX.Core.SplashScreen and
Xamarin.AndroidX.Browser. Neither is pulled transitively by
Avalonia.Android 12.1.1 (its nuspec declares only AppCompat +
Window), and they are not referenced anywhere in PostIt code.
- Resources/values-v31/styles.xml: drop the windowSplashScreen*
items and the 'postSplashScreenTheme' reference, which require
the dropped SplashScreen package. We fall back to the system
splash screen on Android 12+ devices; a custom one can come
back when we add it on purpose.
