revert update of minimum browser support for firefox and safari

test-plan:
* in safari 5, verify browser warning does not display
* in firefox 17, verify browser warning does not display

Change-Id: I15866e476181e76837b15eb749cde52da84e6e52
Reviewed-on: https://gerrit.instructure.com/30062
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Cameron Matheson <cameron@instructure.com>
Product-Review: Bryan Madsen <bryan@instructure.com>
QA-Review: Bryan Madsen <bryan@instructure.com>