delete references of deprecated chat

frappe/desk/form/assign_to.py

@@ -160,7 +160,4 @@ def notify_assignment(assigned_by, owner, doc_type, doc_name, action='CLOSE',
 			'notify': notify
 		}
 
-	arg["parenttype"] = "Assignment"
-
-	from frappe.desk.page.chat import chat
-	chat.post(**arg)
+	arg["parenttype"] = "Assignment"

frappe/share.py

@@ -148,7 +148,4 @@ def notify_assignment(shared_by, doc_type, doc_name, description=None, notify=0)
 		'txt': _("A new document {0} has been shared by with you {1}.").format(document,
 				shared_by),
 		'notify': notify
-	}
-
-	from frappe.desk.page.chat import chat
-	chat.post(**arg)
+	}