Disable the customization of linter severities for ArcanistCommitLinter

Summary: The expectation is that this linter only raises errors.

Test Plan: This is mostly theoretical.

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: Korvin, epriestley

Differential Revision: https://secure.phabricator.com/D11331

src/lint/linter/ArcanistCommitLinter.php

@@ -30,6 +30,10 @@ final class ArcanistCommitLinter extends ArcanistLinter {
     );
   }
 
+  protected function canCustomizeLintSeverities() {
+    return false;
+  }
+
   public function lintPath($path) {
     if ($this->getEngine()->getCommitHookMode()) {
       $this->lintNoCommit($path);