R1:c02f750267f8

Remove dot/Graphviz Remarkup rule

Summary: Ref T9408. This rule is unsafe in principle, and a practical vulnerability has been found by a security researcher.

Test Plan: `grep`

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T9408

Differential Revision: https://secure.phabricator.com/D14103