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