Removed i18n as a Manage category
As mentioned in #3657 (closed), i18n is a community-led effort to translate the GitLab application. It's worth tracking in an epic, but it is not a "high-level capabilities that may be a standalone product at another company" as we've defined on the categories page. It also does not have discernible maturity levels like other categories.
Edited by Jeremy Watson (ex-GitLab)