:fire: Remove splash screen

[Cynnexis]

Describe the bug
The splash screen support is deprecated. Please remove it.

To Reproduce
Steps to reproduce the behavior:

1. Run the command flutter run --release in a terminal at the root of the project.
2. See following error:

   W/FlutterActivityAndFragmentDelegate(27459): A splash screen was provided to Flutter, but this is deprecated. See flutter.dev/go/android-splash-migration for migration steps.
   

Expected behavior
No warning in the console when running the app.

Desktop (please complete the following information):

• OS: Windows 10
• Browser: Firefox
• Version: 99.0.1

Additional context
See https://docs.flutter.dev/development/ui/advanced/splash-screen#migrating-from-manifest--activity-defined-custom-splash-screens for more info