Remove the ArcanistScalaSBTLinter

Summary: As discussed in D9097, the ArcanistScalaSBTLinter isn't really a linter. Eventually we should add support for a proper Scala linter, but I think that supporting the ArcanistScalaSBTLinter as-is is more effort than it is worth.

Test Plan: N/A

Reviewers: epriestley, Blessed Reviewers

Reviewed By: epriestley, Blessed Reviewers

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D9664