Remove request fields ignored by GitLab API

This removes some fields that our Git hooks were sending to the GitLab internal API during the Git hooks.

These fields were made obsolete by the Gitaly migration. If you look in the Rails code you can see they are no longer used anyway: https://gitlab.com/gitlab-org/gitlab/-/blob/fb46b18bd5324fae08e78a2486b39b82148e611d/lib/gitlab/git/hook_env.rb#L16-19

Having these fields in the request doesn't hurt, strictly, but it's confusing for anyone trying to understand how this stuff works. We could have deleted these lines over a year ago already, probably.