Merge branch '417852-remove-unneeded-button-classes' into 'master'

Remove redundant button styling classes

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/149705



Merged-by: Coung Ngo <cngo@gitlab.com>
Approved-by: Coung Ngo <cngo@gitlab.com>
Co-authored-by: Mark Florian <mflorian@gitlab.com>