don't keep generated locales in git

closes CNVS-12609

test plan:
- make sure rake i18n:generate still works
- basic regression of i18n in canvas

Change-Id: I882c7b6f197d65aa673a22225ae6a87ee4431aa0
Reviewed-on: https://gerrit.instructure.com/33760
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Jon Jensen <jon@instructure.com>
QA-Review: Amber Taniuchi <amber@instructure.com>
Product-Review: Simon Williams <simon@instructure.com>