[native] Stop persisting connection in keyserverStore

Summary:
issue: https://linear.app/comm/issue/ENG-4460/refactor-connection-field
We don't want to persist the connection field, but we do want to persist the rest of keyserverStore.

Test Plan:
Checked that the in and out actions work as expected, checked that in rehydrated keyserverStore connection has the value of the default connection
info.

Reviewers: michal, kamil

Reviewed By: kamil

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D9024