Bumping gaia.json for 3 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/ce7e61bd80ab
Author: Ryan VanderMeulen <rvandermeulen@mozilla.com>
Desc: Revert "Merge pull request #20256 from DouglasSherk/1019546-dialer-contacts-overlap"

This reverts commit c0b942c20e9b9d887401ffc19eac8b3d8c7dd30f, reversing
changes made to 641f7d1ac37d4321f69ccb0db4ac3aedcaddadfd.

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https://hg.mozilla.org/integration/gaia-central/rev/4cb955b006da
Author: Ryan VanderMeulen <rvandermeulen@mozilla.com>
Desc: Merge pull request #20422 from flodolo/bug1022781

Bug 1022781 - Remove unnecessary plural form in Conference Call header

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https://hg.mozilla.org/integration/gaia-central/rev/19eaa50d64a1
Author: Francesco Lodolo (:flod) <flod@lodolo.net>
Desc: Bug 1022781 - Remove unnecessary plural form in Conference Call header
Bumping manifests a=b2g-bump