Fix bad dependency.

The `vtkSMTKMeshingExt` library is not needed and not always present.
Status Job ID Name Coverage
  External
passed cdash

passed ghostflow-branch-check-master

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

00:00:51

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

00:03:12

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

00:00:04

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

00:03:14

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

00:03:13

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

00:06:31

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

1010:49:49

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

00:00:28

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

00:04:02

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

00:03:58

passed cdash