Bumping gaia.json for 4 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/021f8aa70d8d
Author: Gareth Aye <gaye@mozilla.com>
Desc: Merge pull request #24898 from gaye/re-reland-amd

Bug 1027707 - Re reland amd

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https://hg.mozilla.org/integration/gaia-central/rev/0b20602c3cb1
Author: gaye <gaye@mozilla.com>
Desc: Bug 1027707 - Followup to turn off debug logging for authentication data

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https://hg.mozilla.org/integration/gaia-central/rev/ec08f86a0381
Author: gaye <gaye@mozilla.com>
Desc: Bug 1027707 - jrburke followup to handle PRODUCTION=1 builds using rjs

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https://hg.mozilla.org/integration/gaia-central/rev/a0fc76fc9d3a
Author: gaye <gaye@mozilla.com>
Desc: Revert "Revert "Merge pull request #24733 from gaye/reland-amd""

This reverts commit 1b02818f092d4699a864976729ac924e5f0f9499.
Bumping manifests a=b2g-bump