COMP: Drop invalid custom commands from HDF5

CMake 3.0 introduces policy CMP0040 to diagnose add_custom_command calls
whose TARGET option names a target that does not exist.  Drop such
unused custom commands from HDF5.

Change-Id: Ic1fc58a3e2f171c35a9c055cdeca7bcc484ff837
COMP: Drop missing dependencies of target 'vtkpython_pyc'

CMake 3.0 introduces policy CMP0046 to diagnose missing dependencies
named by the add_dependencies command.  Drop such unused dependencies
from Wrapping/Python.

Change-Id: I60a976f92b51c10313910c12fbede46e90be9a96