Remove coverage monkeypatch for measuring coverage across process boundaries

[msabramo]

This came up as an issue in dealing with #106.

https://github.com/nickstenning/honcho/blob/9550461068ae792ed20083903d7fca97f2c010f0/honcho/test/unit/test_manager.py#L10

@nedbat suspects that we can probably replace with something better after looking at http://nedbatchelder.com/code/coverage/subprocess.html

[nickstenning]

Closed by dd159ba6a7b614c560e823275c319a386c35b00d.