Move marketing site language use to SaaS only
Currently marketing_site_language that observes the glm_source
parameter to set the preferred language exists for all GitLab instances and only needs to exist for SaaS(GitLab.com) since that parameter will only be set by our marketing site that is only observed in the code.
Originally implemented in Honor preferred language from browser as user e... (#418290 - closed)
Solution
Move it to SaaS only