Remove block opacity when changing visibility

This MR reverts f064d4bb (which did
not fix the bug it was intended to fix) and instead removes a block's
opacity entry when changing a block's visibility to false.

Because visibility and opacity are orthogonal in
vtkSMTKResourceRepresentation, it was originally possible for a block
to have a visibility of 0 and an opacity of 1. The block would
therefore not render, but it would still occlude other blocks. This MR
tethers (in)visibility and opacity, so invisible objects do not have
an opacity entry in the class's BlockOpacities map.
Status Job ID Name Coverage
  External
passed cdash

passed ghostflow-branch-check-master

pending smtk@master-junction-osx-shared-release+remus
failed smtk@master-kerbin-windows-shared-release+examples+remus

passed smtk@master-moho-linux-shared-relwithdebinfo+examples+private+remus

passed smtk@master-moho-linux-shared-relwithdebinfo+examples+python3+remus+vtk

passed smtk@master-moho-linux-shared-relwithdebinfo+examples+remus

passed smtk@master-moho-linux-shared-relwithdebinfo+examples+remus+vtk

passed smtk@master-norkit-osx-shared-release+examples+matplotlib

passed smtk@master-praxis-windows-shared-release

passed smtk@master-talosiv-osx-shared-release+examples+matplotlib

failed smtk@master-tatooine-osx-shared-release+examples+matplotlib

failed smtk@master-tatooine-osx-shared-release+examples+matplotlib+private

passed cdash

failed smtk@master-kerbin-windows-shared-release+examples+remus

00:01:34

passed smtk@master-moho-linux-shared-relwithdebinfo+examples+private+remus

00:11:10

passed smtk@master-moho-linux-shared-relwithdebinfo+examples+python3+remus+vtk

00:00:40

passed smtk@master-moho-linux-shared-relwithdebinfo+examples+remus

00:11:08

passed smtk@master-moho-linux-shared-relwithdebinfo+examples+remus+vtk

00:09:20

passed smtk@master-norkit-osx-shared-release+examples+matplotlib

00:02:50

passed smtk@master-praxis-windows-shared-release

00:01:35

passed smtk@master-talosiv-osx-shared-release+examples+matplotlib

00:02:59

failed smtk@master-tatooine-osx-shared-release+examples+matplotlib

00:05:16

failed smtk@master-tatooine-osx-shared-release+examples+matplotlib+private

00:01:59