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

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https://hg.mozilla.org/integration/gaia-central/rev/6affb05ae328
Author: vingtetun <21@vingtetun.org>
Desc: Merge pull request #16437 from heycam/rm-prefixes

Bug 974266 - Remove property prefixes that are no longer needed.

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https://hg.mozilla.org/integration/gaia-central/rev/21343fab8888
Author: Cameron McCormack <cam@mcc.id.au>
Desc: Bug 974266 - Remove property prefixes that are no longer needed. r=21
Bumping manifests a=b2g-bump