perf(tutorials): skip some writes in export_vtk_tutorial.py

[wpbonelli]

Since exporting a transient array looks the same as exporting a normal array, I removed that cell. And commented out 2 more write statements that were each taking ~45s. This brings the runtime from >2 minutes down to ~30 seconds on my machine.

The goal here (eventually) is to get the notebooks to run fast enough for the RTD build service, so we don't have to run them on GH actions and then upload to RTD. Also just for convenience — it seems a bit daunting and unexpected for a tutorial notebook to spin for minutes. Is there a different transient model we could swap into the VTK export example to avoid commenting out the write statements?

The next slowest are

142.58s call     test_notebooks.py::test_notebooks[/Users/wbonelli/dev/flopy/.docs/Notebooks/swi2package_example5.py]
117.58s call     test_notebooks.py::test_notebooks[/Users/wbonelli/dev/flopy/.docs/Notebooks/swi2package_example2.py]
66.68s call     test_notebooks.py::test_notebooks[/Users/wbonelli/dev/flopy/.docs/Notebooks/plot_array_example.py]
65.77s call     test_notebooks.py::test_notebooks[/Users/wbonelli/dev/flopy/.docs/Notebooks/feat_working_stack_examples.py]
63.09s call     test_notebooks.py::test_notebooks[/Users/wbonelli/dev/flopy/.docs/Notebooks/plot_cross_section_example.py]
42.40s call     test_notebooks.py::test_notebooks[/Users/wbonelli/dev/flopy/.docs/Notebooks/raster_intersection_example.py]

But this PR does not attempt anything on these yet

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 76.3%. Comparing base (bb9824e) to head (efbd104).
Report is 44 commits behind head on develop.

Additional details and impacted files

@@            Coverage Diff            @@
##           develop   #2432     +/-   ##
=========================================
+ Coverage     68.4%   76.3%   +7.8%     
=========================================
  Files          294     294             
  Lines        59390   59934    +544     
=========================================
+ Hits         40652   45739   +5087     
+ Misses       18738   14195   -4543     

see 248 files with indirect coverage changes

[langevin-usgs]

Thanks, @wpbonelli. This looks good. Agreed on effort to speed this all up.