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

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https://hg.mozilla.org/integration/gaia-central/rev/a49cc4c96039
Author: Yuren Ju <yurenju@gmail.com>
Desc: Revert "Bug 904105- part 2: create firefox extension"

This reverts commit 618299d02e6d8c613ca0f6f8efe9a1be69d76c9b.