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

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https://hg.mozilla.org/integration/gaia-central/rev/a4d9c73e176e
Author: Ryan VanderMeulen <ryanvm@gmail.com>
Desc: Revert "Merge pull request #14360 from samjoch/bug-924624-UserStoryAddEdgeGesturesToFTETutorial"

This reverts commit 0602aa7814a65448c17c2119d026da66df19490b, reversing
changes made to 339d3c6801e690232e80dae1ab1d701c025992ff.
Bumping manifests a=b2g-bump