NAS-130901 / 25.04 / Remove REST from test_230_idmap

[aiden3c]

I've removed querying after we create the new idmap as deleting would fail if the creation failed silently somehow.
Also renamed the file.

As always, here's a passing test (look for test_230_idmap as I hadn't changed the name of the test during this run)

[bugclerk]

Jira URL: https://ixsystems.atlassian.net/browse/NAS-130901

[creatorcary]

You could still replicate test_03 by importing ValidationErrors from truenas_api_client.exc and doing something like

with pytest.raises(ValidationErrors, match=f'IdmapDomain {idmap_id} does not exist'):
    call('idmap.get_instance', idmap_id)

if you wanted to

[aiden3c]

Running new tests, will merge once it's passed!

[bugclerk]

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