[BUG] The simulation option `pml_auto=True` does not seem to affect kSpaceFirstOrderAS

[waltsims]

Describe the bug When running an axis-symmetric simulation with the simulation option pml_auto=True, the following warning is still raised:

WARNING:root:Highest prime factors in each dimension are [  3 109]
WARNING:root:Use dimension sizes with lower prime factors to improve speed

To Reproduce Steps to reproduce the behavior:

1. Go to the at_focused_bowl_AS example and run the ipython notebook.
2. Click on update the simulation arguments to

simulation_options = SimulationOptions(
    simulation_type=SimulationType.AXISYMMETRIC,
    data_cast='single',
    data_recast=False,
    save_to_disk=True,
    save_to_disk_exit=False,
    pml_inside=False,
    pml_auto=True)

4. run the notebook
5. See warning

Expected behavior Expected behavior is that the plm_auto option optimizes the PML size such that the highest prime factors are low and thus optimize runtime.