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

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https://hg.mozilla.org/integration/gaia-central/rev/c7df3a8049fe
Author: Anthony Ricaud <anthony@ricaud.me>
Desc: Revert "Merge pull request #17386 from nucliweb/973827-Power-button-modal"

This reverts commit 3ba39ebd3fd4613640f9477898a008580ef8fb41, reversing
changes made to ad3ff4d8515803a5467957f3c39faf83653b5510.
Bumping manifests a=b2g-bump