converts assignments/_assignments_list_content js_block into js_bundle

test plan:
* regression test assignments

Change-Id: Idc5aa62d5369acc215112a384a54dfa04fb22615
Reviewed-on: https://gerrit.instructure.com/29176
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Jon Jensen <jon@instructure.com>
QA-Review: Caleb Guanzon <cguanzon@instructure.com>
Product-Review: Landon Wilkins <lwilkins@instructure.com>