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

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https://hg.mozilla.org/integration/gaia-central/rev/ac70186f8d7e
Author: Carsten Book -Tomcat- <cbook@mozilla.com>
Desc: Revert "Bug 961800 - Implement Child Window Factory" for Gaia UI Test Bustage

This reverts commit 0cd5228663d8563831f0156e85ae8225d2004a3c.
Bumping manifests a=b2g-bump