Remove max_bytes_used test from haddock test cases

Summary:
as these are not very reliable, and the advice to make them reliable
is hard to apply to them.

(This is just my practicing phab...)

Test Plan: validate

Reviewers: austin

Reviewed By: austin

Subscribers: carter, ezyang, simonmar

Differential Revision: https://phabricator.haskell.org/D188

GHC Trac Issues: #9535