Bumping gaia.json for 1 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/787e0db2b536
Author: BavarianTomcat <tomcat@mozilla.com>
Desc: Revert "Bug 923452 - SV: Maximum length of SMS to convert to MMS customization by SIM" for gaia unit test failures

This reverts commit 48274bd301449dccf96c42e6dd9cfe39598865d3.
Bumping manifests a=b2g-bump