Do not generate assignees node variable

In Studio, when creating a workflow task, an assignees node variable is automatically created

This is confusing users:

• They think it has to be used instead of the actual assignees field in the task configuration
• Or they think it's needed for technical reasons
• It's even worse with Designer, when people generate the layout it creates an element for the assignees variable and people expect it to define who you're going to assign this task to

TODO
Remove the assignees node variable when drag and dropping new workflow nodes (= no impact on existing, only for new nodes created)

AC

• When I drag and drop a workflow task of any kind and look at the node variables, the list is empty