Remove import vrml from Supervisor controller

[stefaniapedrazzi]

In R2022b we just removed the functionality to import VRML files from the GUI. But it is still possible to import a ".wrl" file using the wb_supervisor_field_import_mf_node.

This functionality is not documented, but for consistency it might be better to remove it as well from the Supervisor controller and to promote the use of different import methods.