Minor: consolidate GroupByOrderMode::None

[alamb]

Which issue does this PR close?

Related to #7129

Rationale for this change

Inspired by @mustafasrepo 's comment https://github.com/apache/arrow-datafusion/pull/7129/files#r1278576304 about Option<GroupByOrderMode> being redundant with GroupByOrderMode::None here I tried the alternate approach to see what it would look like

I am not sure which I prefer but figured I would put it up for review in case other people liked this

What changes are included in this PR?

1. Change Option<GroupByOrderMode> to GroupByOrderMode

Are these changes tested?

Covered by existing tests

Are there any user-facing changes?

No

[mustafasrepo]

I think we could have pursued, this approach. Do you think that this is not a good change?

[alamb]

I think we could have pursued, this approach. Do you think that this is not a good change?

Sorry I should have been more explicit. Basically I closed it because

1. It was going to conflict with [bug]: Fix multi partition wrong column requirement bug  #7129
2. While I prefer this approach rather than Option I think that was just a personal preference and I don't think there is any technical reason to prefer Option vs the approach in this PR.
3. I was running out of time yesterday and was feeling overwhelmed by too many other open threads of thought to pursue this one

So I do think it is a good change but not valuable enough that I plan to pursue at this time