Merge branch 'eduardosanz/login-tabs' into 'master'

Remove .borderless and .nav-links-unboxed

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/143933



Merged-by: David Pisek <dpisek@gitlab.com>
Approved-by: David Pisek <dpisek@gitlab.com>
Approved-by: Rudy Crespo <rcrespo@gitlab.com>
Co-authored-by: Eduardo Sanz García <esanz-garcia@gitlab.com>