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

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https://hg.mozilla.org/integration/gaia-central/rev/021468251ee1
Author: Gareth Aye <gaye@mozilla.com>
Desc: Merge pull request #20013 from gaye/backout-963394

Revert "Merge pull request #19058 from evanxd/bug-963394"

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https://hg.mozilla.org/integration/gaia-central/rev/112a24439eeb
Author: gaye <gaye@mozilla.com>
Desc: Revert "Merge pull request #19058 from evanxd/bug-963394"

This reverts commit 793b7eaec42b0226395f87e87be14c6d50c36a49, reversing
changes made to 876d97f622292948e2f6a32a3996ed2167eab217.
Bumping manifests a=b2g-bump