Removes tmp_index_project_statistics_updated_at from project statistics

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/155997



Merged-by: Leonardo da Rosa <ldarosa@gitlab.com>
Approved-by: Bojan Marjanovic <bmarjanovic@gitlab.com>
Approved-by: Leonardo da Rosa <ldarosa@gitlab.com>
Reviewed-by: Leonardo da Rosa <ldarosa@gitlab.com>
Co-authored-by: Vijay Hawoldar <vhawoldar@gitlab.com>