Don't add hint margins for XOM exercises
Don't add hint margins for XOM exercises

Summary:
We want our hints on mobile devices (in XOM) to be flush to the left. This diff removes the left
margin that was added to the new exercises framework.

Test Plan:
- Substate into webapp.
- Enable XOM.
- Open up an exercise on a phone or tablet.
- Take a hint.
    - Verify that there is no left margin.

Reviewers: samiskin

Reviewed By: samiskin

Subscribers: jared

Differential Revision: https://phabricator.khanacademy.org/D29611

learningequality/perseus,ariabuckles/perseus,ariabuckles/perseus,ariabuckles/perseus,learningequality/perseus,ariabuckles/perseus