Remove legacy mobile documentation (#586)

Author: mpbw2

docs/architecture/mobile-clients/net-maui-legacy/index.mdx

@@ -11,8 +11,3 @@ See the [Android Mobile app](./android/index.md) page to set up a Kotlin develop
 ## iOS Development
 
 See the [iOS Mobile app](./ios/index.md) page to set up a Swift development environment.
-
-## .NET MAUI Development (legacy)
-
-See the [.NET MAUI app](./net-maui-legacy/index.md) page to set up a .NET MAUI development
-environment.