Merge branch '366605-remove-alert-override-css' into 'master'

Remove unused alert overwrite css

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/127547



Merged-by: Frédéric Caplette <fcaplette@gitlab.com>
Approved-by: Ammar Alakkad <aalakkad@gitlab.com>
Approved-by: Frédéric Caplette <fcaplette@gitlab.com>
Co-authored-by: Alexander Turinske <aturinske@gitlab.com>