Remove ff `sidebar_refactor` from views and remove flag [RUN AS-IF-FOSS]

What does this MR do?

This is a continuation of !63850 (merged). In that MR we removed the feature flag from the BE files.

In this MR we're removing the feature flag from the views, making some refactors, and completely removing the feature flag config files..

Does this MR meet the acceptance criteria?

Conformity

• I have included changelog trailers, or none are needed. (Does this MR need a changelog?)
• I have properly separated EE content from FOSS, or this MR is FOSS only. (Where should EE code go?)
• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.
• This change is backwards compatible across updates, or this does not apply.

Related to #326111 (closed)