Less verbose logging.

Previously, every unit test spat out the lines:

295: 2020-11-20 15:10:03.166 (   0.001s) [main thread     ]            Logging.cxx:131   Info| Logging initialized.
295: 2020-11-20 15:10:03.166 (   0.001s) [main thread     ]         Initialize.cxx:280   Info| Unknown option to Initialize: --data-dir=/Users/4nt/vtk-m/data/data
295: 
295: 2020-11-20 15:10:03.166 (   0.001s) [main thread     ]         Initialize.cxx:280   Info| Unknown option to Initialize: --baseline-dir=/Users/4nt/vtk-m/data/baseline

This removes these statements, as it appears that unknown options to initial aren't really a problem, and stating that logging is initialized is unhelpful, as the lines printed before it:

295: date       time         ( uptime  ) [ thread name/id ]                   file:line     v| 
295: 2020-11-20 15:10:03.166 (   0.001s) [main thread     ]             loguru.cpp:591   Info| arguments: UnitTestPixelTypes --device=serial -v INFO --data-dir=/Users/4nt/vtk-m/data/data --baseline-dir=/Users/4nt/vtk-m/data/baseline
295: 2020-11-20 15:10:03.166 (   0.001s) [main thread     ]             loguru.cpp:594   Info| Current dir: /Users/4nt/vtk-m/build/vtkm/io/testing
295: 2020-11-20 15:10:03.166 (   0.001s) [main thread     ]             loguru.cpp:596   Info| stderr verbosity: 0
295: 2020-11-20 15:10:03.166 (   0.001s) [main thread     ]             loguru.cpp:597   Info| -----------------------------------

make that clear.

Also, clean up unit test which I used to validate this MR against.