converts assignments/_wizard_box js_block into js_bundle

test plan:
* regression test assignments wizard box

Change-Id: I333aa09367510bbd555bdcbdef084097df0eb6f1
Reviewed-on: https://gerrit.instructure.com/29171
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Stanley Stuart <stanley@instructure.com>
QA-Review: Caleb Guanzon <cguanzon@instructure.com>
Product-Review: Landon Wilkins <lwilkins@instructure.com>