Remove DesignKit package (#1886)

- Move button styles to Compound
- Rename text style to AuthenticationTextStyle as its only in the auth flow.
- Add the brand colour locally for now until its included in Compound.

* Update snapshots.

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Co-authored-by: Stefan Ceriu <stefan.ceriu@gmail.com>

ElementX/Sources/Generated/Assets.swift

@@ -27,6 +27,7 @@ internal enum Asset {
   internal enum Colors {
     internal static let accentColor = ColorAsset(name: "colors/accent-color")
     internal static let backgroundColor = ColorAsset(name: "colors/background-color")
+    internal static let brandColor = ColorAsset(name: "colors/brand-color")
     internal static let grabber = ColorAsset(name: "colors/grabber")
   }
   internal enum Images {