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

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https://hg.mozilla.org/integration/gaia-central/rev/2bc7e9e7f50b
Author: vingtetun <21@vingtetun.org>
Desc: Merge pull request #21179 from vingtetun/backout-bug1027438

Revert "Bug 1027438 - [LockScreen][System] Change the old locking events...

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https://hg.mozilla.org/integration/gaia-central/rev/c1576ffa5dc1
Author: Vivien Nicolas <vnicolas@mozilla.com>
Desc: Revert "Bug 1027438 - [LockScreen][System] Change the old locking events with new window events > remove something missed and fork the event"

This reverts commit 7abe707abb22d3d72752e8d9f730f14a7eb1a7ae.
Bumping manifests a=b2g-bump