Update the `empty_call_test` and `routing_parameter_test` macro so that it can be used for both `gRPC` and `REST`

[parthea]

The empty_call_test macro only supports gRPC. We should update this macro so that it can be used for REST transport as well.

gapic-generator-python/gapic/templates/tests/unit/gapic/%name_%version/%sub/test_macros.j2

Lines 1904 to 1909 in 4c5de87

	{% macro empty_call_test(service, api, transport, is_async) %}
	{# TODO(https://github.com/googleapis/gapic-generator-python/issues/2159):
	Currently this macro only supports gRPC. It should be updated to support REST
	transport as well.
	#}
	{% if 'rest' not in transport %}

The same applies to routing_parameter_test which was introduced in PR #2133