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

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https://hg.mozilla.org/integration/gaia-central/rev/75d97d4b116e
Author: BavarianTomcat <tomcat@mozilla.com>
Desc: Revert "Bug 1097296 - [Window Management] Battery, Signal and time on the status bar will appear behind download update overlay. r=etienne" for test failures

This reverts commit b5516bece85f6588fe1cabc7738d48c031774f7c.
Bumping manifests a=b2g-bump