Refactor list_selector - remove unused fetch

What does this MR do and why?

This MR solves point 1 & 2 of the issue

• removing a variant of a component that will search through subgroups of groups. We briefly used this on Branch rule details page, but realised it's not the a set of groups we need (see: !158253 (merged))
• adding stories for all that component variants

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

I'm pasting a recording of where this component is used in groups variant, just to make sure it's still working.

Before	After
Screen_Recording_2024-07-23_at_12.56.56	Screen_Recording_2024-07-23_at_12.49.39

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. Make sure pipeline passes, especially the component's i spec/frontend/vue_shared/components/list_selector/index_spec.js
2. Run storybook:start and check component stories

Related to #470867 (closed)