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

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https://hg.mozilla.org/integration/gaia-central/rev/93de9c5bcb90
Author: Ryan VanderMeulen <ryanvm@gmail.com>
Desc: Revert "Merge pull request #16992 from etiennesegonzac/bug-980984-incoming-alert-from-system"

This reverts commit 88677ea30dff41d6dc404ab95285d318accdd738, reversing
changes made to 6826cb8e2589651fbe3ec15b4fa9cb9a372de4cf.
Bumping manifests a=b2g-bump