Remove unnecessary html respond

What does this MR do and why?

• Contributes to #351520 (closed)
• Sentry error: https://sentry.gitlab.net/gitlab/gitlabcom/issues/3237376

Problem

Double call of respond_to causes ActionController::RespondToMismatchError

Solution

We already render 404 page for missing formats, because of that we can remove unnecessary responder.

How to set up and validate locally

1. Visit http://127.0.0.1:3000/root/Flight/-/refs/master/logs_tree
2. Confirm to see 404 page
3. Visit http://127.0.0.1:3000/root/Flight/-/refs/master/logs_tree?format=json
4. Confirm to see a json response with a list of files

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.