Don't format "1/" as an ordered list in Remarkup

Summary: See <https://www.facebook.com/dreiss/posts/10152231659206208>. I added this "bizarre Facebook-ism" to the set of ordered list characters in T3797, but apparently the intent of these "1/" lists is to avoid automatic formatting. I don't fully understand any part of this, but this list style is used only at Facebook, and automatically formatting these lists enjoys little support there (25 against, 2 for, 29 neutral).

Test Plan: Updated and executed unit tests.

Reviewers: btrahan, chad, dreiss

Reviewed By: dreiss

Subscribers: aran, epriestley

Differential Revision: https://secure.phabricator.com/D8489