**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
:param gcp_conn_id: The connection ID to use connecting to Google Cloud
        Platform.
    :type gcp_conn_id: str
    :param delegate_to: The account to impersonate, if any.
        For this to work, the service account making the request must have
        domain-wide delegation enabled.
    :type delegate_to: str
    :param poll_sleep: The time in seconds to sleep between polling Google
        Cloud Platform for the dataflow job status while the job is in the
        JOB_STATE_RUNNING state.
    :type poll_sleep: int
    :param job_class: The name of the dataflow job class to be executed, it
        is often not the main class configured in the dataflow jar file.
    :type job_class: str
    :param multiple_jobs: If pipeline creates multiple jobs then monitor all jobs
    :type multiple_jobs: boolean
    :param check_if_running: before running job, validate that a previous run is not in process
    :type check_if_running: CheckJobRunning(IgnoreJob = do not check if running, FinishIfRunning=
        if job is running finish with nothing, WaitForRun= wait until job finished and the run job)
        ``jar``, ``options``, and ``job_name`` are templated so you can use variables in them.
    Note that both
    ``dataflow_default_options`` and ``options`` will be merged to specify pipeline
    execution parameter, and ``dataflow_default_options`` is expected to save
    high-level options, for instances, project and zone information, which
    apply to all dataflow operators in the DAG.
    It's a good practice to define dataflow_* parameters in the default_args of the dag
    like the project, zone and staging location.
    .. code-block:: python
       default_args = {
           'dataflow_default_options': {