Bumping gaia.json for 2 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/9f28e210153f
Author: gasolin <gasolin@gmail.com>
Desc: Merge pull request #23065 from gasolin/issue-1054135-2

Bug 1054135 - [B2G][System] support 24 hour time format for Time picker, r= alive

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https://hg.mozilla.org/integration/gaia-central/rev/55e84819ff04
Author: gasolin <gasolin@gmail.com>
Desc: Bug 1054135 - [B2G][System] support 24 hour time format for Time picker

- remove date_picker since its not used
- fix no existing timepicker case
Bumping manifests a=b2g-bump