Bumping gaia.json for 1 gaia-central revision(s) a=gaia-bump

========

https://hg.mozilla.org/integration/gaia-central/rev/cc4960fff59b
Author: Anthony Ricaud <anthony@ricaud.me>
Desc: Revert "Merge pull request #11989 from MBRSL/eng-mode"

This reverts commit 5cbabfd0447bae12d87fd5e520e245943f847c7e, reversing
changes made to 6b4f0746b30a8685600435ea96808fc4e1671473.

This broke test_persona_app.py test_persona_app.TestPersonaStandard.test_persona_standard_sign_in