Remove pre-commit hooks

Summary: Ref T7674. The arc git-hook-pre-receive and arc svn-hook-pre-commit workflows are being removed.

Test Plan: N/A

Reviewers: epriestley, Blessed Reviewers

Reviewed By: epriestley, Blessed Reviewers

Subscribers: Korvin, epriestley

Maniphest Tasks: T7674

Differential Revision: https://secure.phabricator.com/D12690