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.

---------

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

ElementX/Resources/Assets.xcassets/colors/brand-color.colorset/Contents.json

@@ -0,0 +1,20 @@
+{
+  "colors" : [
+    {
+      "color" : {
+        "color-space" : "srgb",
+        "components" : {
+          "alpha" : "1.000",
+          "blue" : "0.545",
+          "green" : "0.741",
+          "red" : "0.051"
+        }
+      },
+      "idiom" : "universal"
+    }
+  ],
+  "info" : {
+    "author" : "xcode",
+    "version" : 1
+  }
+}