Replace UniqueVisitsHelper with RedisTracking

What does this MR do?

The RedisTracking module has become preferred over the older UniqueVisitsHelper module for visit tracking. This replaces all usage of UniqueVisitsHelper and removes the class.

Does this MR meet the acceptance criteria?

Conformity

• I have included changelog trailers, or none are needed because this is a "developer-facing change". (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.

Related to #325517 (closed)