Bumping gaia.json for 1 gaia-1_2 revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-1_2/rev/8789dd839e82
Author: James Lal <james@lightsofapollo.com>
Desc: Merge pull request #12384 from yurenju/reduce-size

Bug 917144 - remove some apps to reduce image size