Recovered remove_subtree. Easier to use Why3's API with this in

controller.

src/session/controller_itp.ml

@@ -90,6 +90,7 @@ let create_controller config env ses =
     provers;
   c
 
+let remove_subtree = Session_itp.remove_subtree
 
 (* Get children of any without proofattempts *)
 let get_undetached_children_no_pa s any : any list =

src/session/controller_itp.mli

@@ -131,6 +131,10 @@ val add_file : controller -> ?format:Env.fformat -> string -> unit
 (** [add_fil cont ?fmt fname] parses the source file
     [fname] and add the resulting theories to the session of [cont] *)
 
+val remove_subtree: controller -> any -> removed:notifier ->
+  notification:notifier -> unit
+(** Mapping to Session_itp.remove_subtree. Used for code using Why3's API *)
+
 val get_undetached_children_no_pa: Session_itp.session -> any -> any list