account: refactor unregistering logic

This patch removes the callback argument to the doUnregister function,
which wasn't really needed since it was always called right before
returning from the function.

The patch also removes all calls to the shutdownConnections function
outside of doUnregister, and instead adds a boolean argument to
doUnregister to allow the caller to specify if they want the connections
to be shut down. This is a preparatory step for fixing the bug described
in the GitLab issue linked below.

GitLab: #1095
Change-Id: Ic78659f2e00684fd1db91c0ee3cf894a53d558ce