PUT /omicron-zone -- stop provisioning datasets!

[smklein]

This is a historical artifact -- we used to provision datasets in the PUT /omicron-zone API, but should now be able to rely on reconfigurator's executor to provision necessary datasets. This issue tracks removing the logic in:

omicron/sled-agent/src/sled_agent.rs

Lines 948 to 964 in 7ca80f1

	// TODO(https://github.com/oxidecomputer/omicron/issues/6043):
	// - If these are the set of filesystems, we should also consider
	// removing the ones which are not listed here.
	// - It's probably worth sending a bulk request to the storage system,
	// rather than requesting individual datasets.
	for zone in &requested_zones.zones {
	let Some(dataset_name) = zone.dataset_name() else {
	continue;
	};
	// First, ensure the dataset exists
	let dataset_id = zone.id.into_untyped_uuid();
	self.inner
	.storage
	.upsert_filesystem(dataset_id, dataset_name)
	.await?;
	}

(Or, at least, replacing it with a check that these datasets exist)

[smklein]

Blocked by #6989 , otherwise RSS will presumably break if these lines are changed. RSS will need to request the datasets itself (this is fixed in #7000 )

[smklein]

Re-opening this issue; it's getting reverted by #7157