Bumping gaia.json for 2 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/1ab6b1fdffb8
Author: Kyle Machulis <kyle@nonpolynomial.com>
Desc: Merge pull request #16539 from qdot/revert-971006

Revert "Merge pull request #16321 from vingtetun/bug971006-final"

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https://hg.mozilla.org/integration/gaia-central/rev/7b8d72ef5e1a
Author: Gareth Aye <gaye@mozilla.com>
Desc: Revert "Merge pull request #16321 from vingtetun/bug971006-final"

This reverts commit 19304fe63b26630f95c6f3a7da49349b433d476e, reversing
changes made to b9859b9c2199e1c5b7e4eda220e556a7ff43cd21.

Conflicts:
	apps/system/js/utility_tray.js
	apps/system/test/unit/utility_tray_test.js
Bumping manifests a=b2g-bump