Remove splashscreen blink

[zoontek]

Hi 👋

react-native-bootsplash author here. I noticed, when using your app, that the splash screen implem doesn't wait for the first render to hide the native splash. This result in a white flash, which is not great given the fact that it's our first experience with the app.

This PR fixes this (without switching lib, I only removed react-native-splash-screen as it's unused and autolinked / built for nothing)

Before (notice the blink) 👇

https://github.com/bluesky-social/social-app/assets/1902323/a2279214-fce7-46cf-8f8d-9816af8440b8

After 👇

https://github.com/bluesky-social/social-app/assets/1902323/5d38486d-5af9-40a2-b85d-3b87e982ccb6