Remove the `between_uses_list_commits` feature flag

What does this MR do?

On Friday, this FF will have been enabled on .com for a couple of days at 100%. Rollout details are in #337960 (closed) , but it is safe to remove it now.

CommitsBetween is obsoleted by ListCommits, and is more amenable to commit limiting, which will come in a later commit.

It was never default_enabled: true, so this MR contains a changelog entry.

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 added/updated documentation, or it's not needed. (Is documentation required?)
• I have properly separated EE content from FOSS, or this MR is FOSS only. (Where should EE code go?)
• I have added information for database reviewers in the MR description, or it's not needed. (Does this MR have database related changes?)
• 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.

Availability and Testing

• I have added/updated tests following the Testing Guide, or it's not needed. (Consider all test levels. See the Test Planning Process.)
• I have tested this MR in all supported browsers, or it's not needed.
• I have informed the Infrastructure department of a default or new setting change per definition of done, or it's not needed.

Closes #337960 (closed)