Cleanup - removing duplicate "hyperactor book" copy. (meta-pytorch#819)

Summary:
Pull Request resolved: meta-pytorch#819

As part of the larger Monarch documentation effort, the hyperactor book was moved into docs/source/books/.  We checked this was okay with the larger group.  This diff is just to clean up the now-duplicate original copy.

Reviewed By: dcci

Differential Revision: D80030132

fbshipit-source-id: 9b2dc710f3d300492db3a55c06ac262c0b010398

Author: johnwhumphreys