Deprecate pubsub::IAMPolicyOptions

[dbolduc]

This API is irrelevant now that we have native mixin support in pubsub. We should deprecate it, and remove/update any instances of it in our repo (e.g. in samples).

google-cloud-cpp/google/cloud/pubsub/options.h

Lines 415 to 429 in a695357

	/**
	* Convenience function to initialize a
	* `google::cloud::iam::IAMPolicyConnection`.
	*
	* To manage the IAM policies of Pub/Sub resources you need to configure the
	* `google::cloud::IAMPolicyClient` to use `pubsub.googleapis.com` as the
	* `google::cloud::EndpointOption` and `google::cloud::AuthorityOption`.
	*
	* This function returns an object that is initialized with these values, you
	* can provide additional configuration, or override some of the values before
	* passing the object to `google::cloud::iam::MakeIAMPolicyConnection`.
	*
	* @ingroup google-cloud-pubsub-options
	*/
	Options IAMPolicyOptions(Options opts = {});