Revert "Merge pull request #695 from github/detect-prose"

This reverts commit 80321272b12ea7b1346e8ebd8ac26b41a97257cd, reversing
changes made to 02500d38305458877482d8c4756e311cf1eaaf6a.
Merge pull request #746 from tnm/no-prose

Revert "Merge pull request #695 from github/detect-prose"