options: Stop using Houdini's Alembic from 17.5+
options: Stop using Houdini's Alembic from 17.5+

Houdini is now using it's own openexr with the _sidefx suffix but
not shipping the python bindings which are used across several other projects
( alembic, openimageio etc ). From Houdini 17.5 onward we will be using our
own alembic lib and openexr binding.

appleseedhq/cortex,appleseedhq/cortex,appleseedhq/cortex