Remove transport client from tests

[rjernst]

This commit removes testing infrastructure for using the transport
client.

[elasticmachine]

Pinging @elastic/es-core-infra

[jaymode]

@rjernst and I discussed this. This test is testing functionality that is currently only used for the transport client as far as I can see. This is based on the following code:

elasticsearch/server/src/main/java/org/elasticsearch/cluster/ClusterState.java

Lines 133 to 136 in a15f1ee

	if (custom.getRequiredFeature().isPresent()) {
	final String requiredFeature = custom.getRequiredFeature().get();
	// if it is a transport client we are lenient yet for a connected node it must have the required feature
	return out.hasFeature(requiredFeature) || out.hasFeature(TransportClient.TRANSPORT_CLIENT_FEATURE) == false;

At this point in time, the removal of the transport client leaves us with the NodeClient but since the NodeClient is a node, the node must have the same plugins/features that the other nodes have. Given this, I do not see a way for this test to continue to be valid without the transport client. In the future, we may decide to use the feature aware logic for remote cluster connections if we need to serialize the cluster state but this is not in place today which is why I think removal of this test is ok.

@jasontedor is this ok with you?

[jasontedor]

That's fine with me. Thanks for checking.

[jaymode]

LGTM