Remove the ArcanistConduitLinter

Summary: This linter is a relic from Facebook days. As Harbormaster becomes more useful (T1049) this linter should become obsolete. Instead of modernising this linter to be compatible with modern infrastructure, it is easier to just let it die.

Test Plan: N/A

Reviewers: Blessed Reviewers, epriestley

Reviewed By: Blessed Reviewers, epriestley

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D10533