remove dead code from plugins/_facebook_settings

test plan:
* regression test facebook settings plugin

Change-Id: I6e5e1648f85057a4f70cae5904b68f418eb782c4
Reviewed-on: https://gerrit.instructure.com/29138
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Jon Jensen <jon@instructure.com>
Product-Review: Marc LeGendre <marc@instructure.com>
QA-Review: Marc LeGendre <marc@instructure.com>