Bumping gaia.json for 2 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/4b0bc53d5c37
Author: Jared Hirsch <ohai@6a68.net>
Desc: Merge pull request #19086 from 6a68/bug-994725-fxa-panel-too-tall

Bug 994725 - FxA panel too tall in FTE

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https://hg.mozilla.org/integration/gaia-central/rev/735af29c750b
Author: Jared Hirsch <ohai@6a68.net>
Desc: Bug 994725 - When SystemDialog instances are displayed, correctly update the height. r=alive

    Also remove some unnecessary FxA-specific CSS.
Bumping manifests a=b2g-bump