Fix T73547: Removed Call To Deprecated Prop

`use_uv_as_generated` has been removed in blender 2.82, but there were 2
add-ons still setting it, what crashes the add-ons.

The affected addons were Sapling Tree and Curve Extra Objects.

Reviewed By: meta-androcto

Differential Revision: https://developer.blender.org/D6739