convert external_content/success js_block into js_bundle

test plan:
* regression test external content success

Change-Id: Ie1cd11908dee14d70f002497c6dd682fb47d5ea3
Reviewed-on: https://gerrit.instructure.com/29152
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>