converts users/registered js_block into js_bundle

test plan:
* regression test user registration

Change-Id: Ib4426f4c4a38a96fe0c2c3327019de796f47cd93
Reviewed-on: https://gerrit.instructure.com/29093
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>