Remove browse controller and views
Remove browse routes

Remove the routes to /browse, and the special-case routes for
/visas-immigration and /business.
Remove browse stylesheet

As these styles are not used elsewhere in Frontend, remove the browse
SASS stylesheet from the asset directories.
Remove visas-immigration redirects

@Shotclog has added these to the router-data repository
(see https://github.gds/gds/router-data/pull/100) so we can safely
remove these from here.
Stop registering routes for browse

Remove the /browse, /business and /visas-immigration paths from
the router registration task.
Merge pull request #627 from alphagov/remove-browse

Remove mainstream browse from Frontend