Simplify RendererProxy and RendererImplementation to Fabric-only

Summary:
Changelog: [internal]

All Meta apps have migrated to Fabric, so we no longer need to support Paper in the renderer infrastructure.

This commit simplifies:
- RendererImplementation.js: Rewritten to only use Fabric renderer
- RendererProxy.fb.js: Removed Paper-related exports
- RendererProxy.js: Updated comment to reflect Fabric variants (profiling vs production)
- FabricRendererImplementationWithProfiling.js: Removed Paper shims
- Jest mock RendererProxy.js: Removed Paper exports

Differential Revision: D101353113

Author: rubennorte

packages/jest-preset/jest/mocks/RendererProxy.js

@@ -23,7 +23,6 @@ const {
   isProfilingRenderer,
   renderElement,
   sendAccessibilityEvent,
-  unmountComponentAtNodeAndRemoveContainer,
   unstable_batchedUpdates,
 } = jest.requireActual<TRendererImplementation>(
   'react-native/Libraries/ReactNative/RendererImplementation',
@@ -40,6 +39,5 @@ export {
   isProfilingRenderer,
   renderElement,
   sendAccessibilityEvent,
-  unmountComponentAtNodeAndRemoveContainer,
   unstable_batchedUpdates,
 };