turn off deprecated dynamic finders for rails 3 and rails 4

closes CNVS-15126

note that find_by_* is not deprecated (but discouraged in
Canvas)

Change-Id: If6421cda0e2ebc48e59c45d07928ef43f586a12c
Reviewed-on: https://gerrit.instructure.com/42286
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Jacob Fugal <jacob@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>