Fix outdated link to MetaMTA web UI in MetaMTA tasks

Summary: Missed this when moving most MetaMTA responsibilities to the CLI. Show the correct command to get data rather than linking to a 404.

Test Plan: {F56733}

Reviewers: wez, btrahan, chad

Reviewed By: chad

CC: aran

Differential Revision: https://secure.phabricator.com/D6846