Now we have a separate map for "git" tracking remote, we can always preserve
the last imported/exported git_refs. The option to restore git-tracking refs
has been removed. Perhaps, --what can be reorganized as --local and --remote
<NAME>.
I've added a boolean flag to the store to ensure that the migration never runs
more than once after the view gets "op restore"-d. I'll probably reorganize the
branches structure to support non-tracking branches later, but updating the
storage format in a single commit would be too involved.
If jj is downgraded, these "git" remote refs would be exported to the Git repo.
Users might have to remove them manually.
