chore(ui): Remove simple theme export (#7381)

Author: alexcarpenter

.changeset/odd-rice-swim.md

@@ -0,0 +1,9 @@
+---
+'@clerk/ui': major
+---
+
+Removes `simple` theme export from UI package in favor of using the `simple` theme via the appearance prop:
+
+```tsx
+<ClerkProvider appearance={{ theme: 'simple' }} />
+```

packages/ui/src/themes/experimental.ts

@@ -1,2 +1 @@
 export { createTheme } from './createTheme';
-export { simple } from './simple';