Bumping gaia.json for 4 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/2c5c1850b482
Author: Jose M. Cantera <jmcanterafonseca@gmail.com>
Desc: Merge pull request #18946 from jmcanterafonseca/move_import_tests2

Bug 1005918 - [FTU-Separation] Move import tests to contacts/test/unit/i...

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https://hg.mozilla.org/integration/gaia-central/rev/2acb34a9b15c
Author: Jose M. Cantera <jmcanterafonseca@gmail.com>
Desc: Bug 1005918 - [FTU-Separation] Move import tests to contacts/test/unit/import

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https://hg.mozilla.org/integration/gaia-central/rev/1198acad7f9d
Author: Salvador de la Puente González <salva@unoyunodiez.com>
Desc: Merge pull request #19052 from Archaeopteryx/costcontrol-stringRemoval

Bug 1001883 - [costcontrol remove unused localizations strings from Firefox OS 2.0. r=salva

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https://hg.mozilla.org/integration/gaia-central/rev/b99f75b0ae84
Author: Sebastian Hengst <archaeopteryx@coole-files.de>
Desc: Bug 1001883 - [costcontrol remove unused localizations strings from Firefox OS 2.0
Bumping manifests a=b2g-bump