Use new AMR plot max level capability

[maximumcats]

PR summary

The support for amr.plot_max_level and amr.small_plot_max_level is added in AMReX-Codes/amrex#2825.

PR checklist

• [x] test suite needs to be run on this PR
• [ ] this PR will change answers in the test suite to more than roundoff level
• [ ] all newly-added functions have docstrings as per the coding conventions
• [ ] the CHANGES file has been updated, if appropriate
• [ ] if appropriate, this change is described in the docs

[zingale]

it looks like the AMReX support for this was added -- do we want to review / merge this?