converts context/roster_user_usage js_block into js_bundle

test plan:
* regression test roster user usage

Change-Id: Idc50b85717ed6f88dd0967aee4b696695509bab5
Reviewed-on: https://gerrit.instructure.com/29159
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Jon Jensen <jon@instructure.com>
QA-Review: Matt Fairbourn <mfairbourn@instructure.com>
Product-Review: Landon Wilkins <lwilkins@instructure.com>