Add fix for h4 font size regression
Add fix for h4 font size regression

fixes: CNVS-26346

This addresses a regression pertaining to new ui <h4> tags displaying
at a small font size.

Issue was caused by selector tags being turned into classes. Fix is to
revert them back to tags in the css.

Test Plan:
- Go into Canvas legacy UI and on a page that uses tiny mce, add an h4
header
- Switch to new UI, h4 header size should remain the same

Screenshot comparisons:

What is was: http://cl.ly/061g3T0k3f1u
What it should be: http://cl.ly/1x1M0M2W2n42

Change-Id: I5766cdb1d18f86d092562a23429b7af4d36a0e69
Reviewed-on: https://gerrit.instructure.com/70034
Tested-by: Jenkins
Reviewed-by: Chris Hart <b82b40b84a2f06957ec9caf1768340bd6b929cc4@instructure.com>
Product-Review: Chris Hart <b82b40b84a2f06957ec9caf1768340bd6b929cc4@instructure.com>
Reviewed-by: Ryan Shaw <ea3cd978650417470535f3a4725b6b5042a6ab59@instructure.com>
QA-Review: Myller de Araujo <e5c7c5e1b7f2ce5e9870cc98ec52b20b3006cb48@instructure.com>

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