**What happened**:

With the new Backport providers, when calling `DataflowCreatePythonJobOperator` with an empty `py_rerquirments` Dataflow commands always launch inside a virtualenv.

**What you expected to happen**:

The Dataflow command should run locally.


airflow/providers/google/cloud/operators/dataflow.py
"""
    Start a Templated Cloud DataFlow batch job. The parameters of the operation
    will be passed to the job.
    :param template: The reference to the DataFlow template.
    :type template: str
    :param job_name: The 'jobName' to use when executing the DataFlow template
        (templated).
    :param options: Map of job runtime environment options.
        .. seealso::
            For more information on possible configurations, look at the API documentation
            `https://cloud.google.com/dataflow/pipelines/specifying-exec-params
            <https://cloud.google.com/dataflow/docs/reference/rest/v1b3/RuntimeEnvironment>`__
    :type options: dict
    :param dataflow_default_options: Map of default job environment options.
    :type dataflow_default_options: dict
    :param parameters: Map of job specific parameters for the template.
    :type parameters: dict
    :param project_id: Optional, the GCP project ID in which to start a job.
        If set to None or missing, the default project_id from the GCP connection is used.
    :type project_id: str
    :param location: Job location.
    :type location: str