FIX-#6446: Stop requiring modin-xgboost approval

[mvashishtha]

What do these changes do?

Stop requiring modin-xgboost approval for xgboost code. Current @modin-project/modin-xgboost members don't know much more than other members of modin-core about the xgboost code.

• first commit message and PR title follow format outlined here

  NOTE: If you edit the PR title to match this format, you need to add another commit (even if it's empty) or amend your last commit for the CI job that checks the PR title to pick up the new PR title.

• passes flake8 modin/ asv_bench/benchmarks scripts/doc_checker.py
• passes black --check modin/ asv_bench/benchmarks scripts/doc_checker.py
• signed commit with git commit -s
• Resolves stop requiring modin-xgboost approval #6446
• tests added and passing
• module layout described at docs/development/architecture.rst is up-to-date

[YarShev]

@mvashishtha, please sign your commit message.

[mvashishtha]

@YarShev done