Clean code related to savedObjectClientContrat that wasn't being used (elastic#200629)

## Summary

Resolves: elastic#197216

Removed all code that wasn't being used in
https://github.com/elastic/kibana/tree/main/src/plugins/saved_objects/public.
Didn't remove the actual client since it's still being used here:
https://github.com/elastic/kibana/blob/dbab2214e9451d3a262007660cc0b7cdcea5307c/src/plugins/home/public/application/kibana_services.ts#L46-L48

Checked everything with `node scripts/type_check`

### Checklist

Check the PR satisfies following conditions. 

Reviewers should verify this PR satisfies this list as well.

- [ ] The PR description includes the appropriate Release Notes section,
and the correct `release_node:*` label is applied per the
[guidelines](https://www.elastic.co/guide/en/kibana/master/contributing.html#kibana-release-notes-process)

---------

Co-authored-by: kibanamachine <[email protected]>

Author: 2 people

src/plugins/saved_objects/public/index.ts

@@ -11,7 +11,7 @@ import { SavedObjectsPublicPlugin } from './plugin';
 
 export type { OnSaveProps, OriginSaveModalProps, SaveModalState, SaveResult } from './save_modal';
 export { SavedObjectSaveModal, SavedObjectSaveModalOrigin, showSaveModal } from './save_modal';
-export { checkForDuplicateTitle, saveWithConfirmation, isErrorNonFatal } from './saved_object';
+export { isErrorNonFatal } from './saved_object';
 export type { SavedObjectSaveOpts, SavedObject, SavedObjectConfig } from './types';
 
 export const plugin = () => new SavedObjectsPublicPlugin();