Bumping gaia.json for 3 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/8549dbaf8758
Author: Florin Strugariu <bebef_1987@yahoo.com>
Desc: Merge pull request #17909 from chirarobert/fix_system_notification

Bug 991088 - Fix test_system_notification_bar.py

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https://hg.mozilla.org/integration/gaia-central/rev/9985cf28a0a1
Author: chirarobert <robert.chira@softvision.ro>
Desc: Bug 991088 - Fix test_system_notification_bar.py

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https://hg.mozilla.org/integration/gaia-central/rev/1f58e112898b
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Revert "Bug 971538 - [System2] Instantiable PermissionManager"

This reverts commit 3b8ede8a3709430135ce557324045e9946c4486f.
Bumping manifests a=b2g-bump