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

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https://hg.mozilla.org/integration/gaia-central/rev/c45d1657b0b4
Author: gasolin <gasolin@gmail.com>
Desc: Merge pull request #16112 from gasolin/issue-968679

Bug 968679 - [settings] add marionette test for Sound panel, r=arthur

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https://hg.mozilla.org/integration/gaia-central/rev/54344bee8df1
Author: gasolin <gasolin@gmail.com>
Desc: Bug 968679 - [settings] add marionette test for Sound panel

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https://hg.mozilla.org/integration/gaia-central/rev/52b318d2511f
Author: Yuren Ju <yurenju@gmail.com>
Desc: Revert "Bug 971648 - Add warning message if there is no"

This reverts commit b8e0bb360d369e7f1bbcf13a6f8d34abd74a0c63.
Bumping manifests a=b2g-bump