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

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https://hg.mozilla.org/integration/gaia-central/rev/ac34484ce7f6
Author: Ryan VanderMeulen <ryanvm@gmail.com>
Desc: Revert "Merge pull request #17807 from huchengtw-moz/system2/Bug_971554-reland-2"

This reverts commit 3c23b5013e62d6f059d9a0b9f9e8c8db0c3aa2fe, reversing
changes made to 716250e989d516c6e0c1bf5bf0d69417428f17c2.

Conflicts:
	apps/system/js/bootstrap.js
Bumping manifests a=b2g-bump