[keyserver][lib][native][web] Remove connection field from redux

Summary:
issue: https://linear.app/comm/issue/ENG-4460/refactor-connection-field
Last step is to remove now not used connection filed from top level of redux

Test Plan: ran yarn flow-all. checked that the migration was succesful.

Reviewers: michal, kamil

Reviewed By: michal

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D8932