Revert "Add an ability to import from github using multiple tokens"

What does this MR do and why?

Reverts !124997 (merged) due to legal concerns as discussed in https://gitlab.com/gitlab-org/gitlab/-/issues/432096

Screenshots or screen recordings

N/A

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

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.