Bumping gaia.json for 4 gaia-central revision(s)

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https://hg.mozilla.org/integration/gaia-central/rev/21d0f4126507
Author: Kyle Machulis <kyle@nonpolynomial.com>
Desc: Merge pull request #12121 from qdot/891725-cellbroadcast-customization

Bug 891725 - Added unit tests for cell broadcast and voicemail customiza...

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https://hg.mozilla.org/integration/gaia-central/rev/d0c799717e7e
Author: Kyle Machulis <kyle@nonpolynomial.com>
Desc: Bug 891725 - Added unit tests for cell broadcast and voicemail customization

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https://hg.mozilla.org/integration/gaia-central/rev/f409d2795cb1
Author: Kyle Machulis <kyle@nonpolynomial.com>
Desc: Bug 898409, 898410: Fixes to operator variant

Fix writable property of navigator.mozPower, remove unused stubPower variable
Change operator variant helper from mobileConnection to iccHelper
mobileConnection seems to be unstable when the sim card is locked. This patch changes operator variant to use IccHelper for fetching mcc/mnc instead.

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https://hg.mozilla.org/integration/gaia-central/rev/bab155b06eb6
Author: Kyle Machulis <kyle@nonpolynomial.com>
Desc: Revert "Revert "Merge pull request #12000 from nullaus/operator-variant""

This reverts commit 8b15a3359fc30f3703808763e976cfcab3812724.