disable audit log searches

refs: CNVS-14114
refs: CNVS-13987

Test Plan:

  Audit Log in Admin tools should have a message saying they have been
  disabled.

  Try to hit an api call to the audit log search and it should return a
  503 with a message that they are disabled.

Change-Id: If3c46f16010d8fd9ace30de885d5572c7299c0ee
Reviewed-on: https://gerrit.instructure.com/37503
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: August Thornton <august@instructure.com>
Reviewed-by: Jacob Fugal <jacob@instructure.com>
Product-Review: Nick Cloward <ncloward@instructure.com>