Remove Lamson documentation

Summary:
Fixes T11054. This project's website has been down for more than a year:

https://github.com/zedshaw/lamson/issues/36

It hasn't received any new commits for three years (March, 2013):

https://github.com/zedshaw/lamson/commits/master

Instructions like this are a good candidate for community ownership rather than upstream maintenance. I don't think we'd accept these instructions upstream today.

Test Plan: grep -i lamson

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T11054

Differential Revision: https://secure.phabricator.com/D15990