Remove spurious storage.fetch from migration
Remove spurious storage.fetch from migration

This should really only be called once, from background.js.

Calling it twice can cause doubled listeners for the registration_done
event, which in turn leads to duplicate post-registration callbacks,
dual sync requests, and an eventual datastore inconsistency.

Fixes #670

// FREEBIE

nrizzio/Signal-Desktop,nrizzio/Signal-Desktop,nrizzio/Signal-Desktop,nrizzio/Signal-Desktop