Add a way to remove existing taxonomies to CPT

[gturpin-dev]

Maybe use unregister_taxonomy_for_object_type() function

This can be a way to unregister a built-in tax for the current CPT

This need some test to check how to work with existing CPT like "post"

Also, care about local storage of PostType and maybe do a diff between this and the get_object_taxonomies() ( again, care with hook priority if we can do something )