Remove response length logging feature

What does this MR do and why?

References

This MR removes the log_response_length feature flag and related implementation. The feature was used to log the size of HTTP responses in both Rails controllers and the API. Since this feature has been evaluated and determined to be unnecessary or no longer needed, we're removing all related code.

Specifically, this MR:

• Removes the log_response_length feature flag definition
• Removes ResponseLogger class from grape logging
• Removes the response byte size calculation from RequestPayloadLogger
• Updates API initialization to no longer include the ResponseLogger
• Updates specs to reflect these changes
• Updates RuboCop todo lists to remove references to deleted files

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Start the application locally
2. Verify logs for controller and API requests no longer contain the response_bytes field
3. Confirm there are no errors related to the removed components in the application logs
4. Run the test suite to ensure all tests pass: bundle exec rspec

MR acceptance checklist

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

Related to #515740 (closed)