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

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https://hg.mozilla.org/integration/gaia-central/rev/6863b2364d38
Author: Francisco Jordano <fjordano@mozilla.com>
Desc: Revert "Bug 1050722 - Reduce overpaint of the contacts app r=arcturus"

This reverts commit 73a49673bb214ecd6905d487066e822f41557aae.

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https://hg.mozilla.org/integration/gaia-central/rev/c50c38008e9f
Author: vingtetun <21@vingtetun.org>
Desc: Merge pull request #23197 from vingtetun/followup.statusdeadcode

Bug 1056046 - Remove statusbar-background dead code. Followup. r=me

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https://hg.mozilla.org/integration/gaia-central/rev/82f7db7814f0
Author: Vivien Nicolas <vnicolas@mozilla.com>
Desc: Bug 1056046 - Remove statusbar-background dead code. Followup. r=me
Bumping manifests a=b2g-bump