Deprecated OPENVDB_BUILD_HOUDINI_SOPS option in favour of OPENVDB_BUILD_HOUDINI_PLUGIN. Improved option comments.
Deprecated OPENVDB_BUILD_HOUDINI_SOPS option in favour of OPENVDB_BUILD_HOUDINI_PLUGIN. Improved option comments.

Signed-off-by: Nick Avramoussis <4c6772d20f21e1f087b814400acc0120202ec49e@dneg.com>

dreamworksanimation/openvdb,dreamworksanimation/openvdb,dreamworksanimation/openvdb,dreamworksanimation/openvdb