Bumping gaia.json for 2 gaia-1_2 revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-1_2/rev/3d9a98142025
Author: cctuan <georgeiscoming@gmail.com>
Desc: Revert "Bug 922462 - Define various size of icons in manifest instead of use buildscript"

This reverts commit 32153515a3eedad26aec89322e02934a0dc06a0f.

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https://hg.mozilla.org/integration/gaia-1_2/rev/5a9252147e52
Author: George <georgeiscoming@gmail.com>
Desc: Merge pull request #12569 from cctuan/922462

Bug 922462 - [Flatfish] use 1.5x icon from manifest for tablet(cherry picked from commit 3c3eda6d93d7329f437b71d03c3d28353f1f3d4c)