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

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https://hg.mozilla.org/integration/gaia-central/rev/c56ef2ae3159
Author: Francisco Jordano <arcturus@ardeenelinfierno.com>
Desc: Revert "Bug 984800 - [MADAI][Contacts] @2.25x assets update for Contacts"

This reverts commit 7e1778e27c0af3add5cc6853b48aae045726ece1.
Bumping manifests a=b2g-bump