refactor: Remove unused confusing code

[MBkkt]

We don't read from this variable except to string.
And we never write to this variable except one case.

So in most case to string will produce incorrect information.

Also this variable isn't really needed, I think it's better to remove it
Even for partitioned write/etc, it's not really used in any ongoing PR

[MBkkt]

@mbasmanova will you review, please?

[mbasmanova]

DistributionType is incomplete, but removing numPartitions is not going to fix that. It needs more information about partitioning. It looks like @hdikeman is wrapping up Connector API changes for Table Write and I should have bandwidth to work on adding TableWrite support to the optimizer. As part of that work I expect to come and revisit DistributionType struct.

[MBkkt]

I think I made it complete in different PR, where partitioning is a function.
But it's quite nontrivial PR that contains different parts, so I decided to start with simple part.

Number of partitions not needed, because count of partitions controlled by optimizer options (numDrivers/numWorkers) when we plan partition.
And it doesn't needed for broadcast/gather, because they have specific behavior.
The only case where is it needed it's write table, but for this case it should be implemented in more abstract way with partition type/function (that internally have number of buckets for hive for an example).
Also table scan, but it's not implement partitioning now

About @hdikeman work, I have PR that implements TableWrite in optimizer, I plan to rebase it after Henry PR with connector api changes will be merged.
So this PR will contains implementation for TableWrite in optimizer.
It will be for TestConnector and for LocalHiveConnectorMetadata but with copartition for hive disabled because it requires some changes in runner.

Does it sounds ok to you?

[mbasmanova]

I have PR that implements TableWrite in optimizer, I plan to rebase it after Henry PR with connector api changes will be merged.

@MBkkt Any chance you could rebase it now? I'd like to start reading it without waiting for Henry's PR to land.

[MBkkt]

I close this PR because this change was accounted in my other, more complete PR: #498