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

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https://hg.mozilla.org/integration/gaia-central/rev/a6cc4e349d0e
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Revert "Bug 1041372 - [User Story] Rocketbar behavior for fullscreen apps with navigation chrome r=vingtetun"

This reverts commit 220224e03d5a4c2da1d33a79fafa87de0b8779c3.
Bumping manifests a=b2g-bump