Bumping gaia.json for 2 gaia-central revision(s)

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https://hg.mozilla.org/integration/gaia-central/rev/9c7d3db26da3
Author: Ryan VanderMeulen <rvandermeulen@mozilla.com>
Desc: Merge pull request #11123 from karlcow/master

826512, 828388, 828394, 828412, 843143 removing ua-override

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https://hg.mozilla.org/integration/gaia-central/rev/b49fc687d5e3
Author: karl <karl+github@la-grange.net>
Desc: 826512, 828388, 828394, 828412, 843143 removing ua-override

b2g/config/gaia.json

@@ -1,4 +1,4 @@
 {
-    "revision": "04e55214d53448c2fed0f03e265c2fe9a8cca62e", 
+    "revision": "9c7d3db26da317a50fecaa63349de604fcd12cb5", 
     "repo_path": "/integration/gaia-central"
 }