This module contained various methods that were forwarded to
Gitlab::Database::Connection. This commit removes these wrappers in
favour of using Gitlab::Database.main instead. This is done to make it
explicit what database connection should be used.

See https://gitlab.com/gitlab-org/gitlab/-/issues/331776 and
https://gitlab.com/gitlab-org/gitlab/-/merge_requests/65262 for more
information.