Remove `username` from `User#sanitize_attrs` callback
Remove `username` from `User#sanitize_attrs` callback

This attribute is since validated against `DynamicPathValidator`, which
has strict requirements for the characters allowed, and should no longer
need to be sanitized in a callback before saving.

This has additional benefits in our test suite, where every creation of
a `User` record was calling `Sanitize.clean` on a username value that
was always clean, since we're the ones generating it.

axilleas/gitlabhq,dreampet/gitlab,jirutka/gitlabhq,dreampet/gitlab,stoplightio/gitlabhq,mmkassem/gitlabhq,jirutka/gitlabhq,axilleas/gitlabhq,jirutka/gitlabhq,dreampet/gitlab,stoplightio/gitlabhq,t-zuehlsdorff/gitlabhq,iiet/iiet-git,t-zuehlsdorff/gitlabhq,dreampet/gitlab,iiet/iiet-git,jirutka/gitlabhq,axilleas/gitlabhq,mmkassem/gitlabhq,stoplightio/gitlabhq,iiet/iiet-git,mmkassem/gitlabhq,mmkassem/gitlabhq,axilleas/gitlabhq,t-zuehlsdorff/gitlabhq,stoplightio/gitlabhq,iiet/iiet-git,t-zuehlsdorff/gitlabhq