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

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https://hg.mozilla.org/integration/gaia-central/rev/2f52419acd2e
Author: Malini Das <thehyperballad@gmail.com>
Desc: Merge pull request #14424 from malini/master

Revert "Merge pull request #14138 from malini/mixin"

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https://hg.mozilla.org/integration/gaia-central/rev/c3c6303cc33d
Author: Malini Das <mdas@mozilla.com>
Desc: Revert "Merge pull request #14138 from malini/mixin"

This reverts commit 091161997bebfc0c2d053339b1c9891c57216920, reversing
changes made to 50c75716ce9740ac1443e02140ae85b4885d47c5.