Update commit version

[eden-ohana]

On the kv migration remove/update the commit version that was added after the parent switch bug on the merge.

const (
   CommitVersionInitial CommitVersion = iota
   CommitVersionParentSwitch

   CurrentCommitVersion = CommitVersionParentSwitch
)

[N-o-Z]

@eden-ohana Do we need it for the release?

[itaiad200]

can't be done - lakeFS kv migration can't change commit IDs