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

b2g/config/gaia.json

@@ -4,6 +4,6 @@
         "remote": "", 
         "branch": ""
     }, 
-    "revision": "1bb11f6f0877e886f23df070a5ba00fbe3eeb9cb", 
+    "revision": "9f28e210153f79f3fb1cfcb211abe43eae4f4c69", 
     "repo_path": "/integration/gaia-central"
 }