Unify doc-strings (remove type/rtype)

As this information is already provided in type hints and we don't need to maintain it in two places.

src/ifcopenshell-python/ifcopenshell/api/structural/add_structural_analysis_model.py

@@ -30,7 +30,6 @@ def add_structural_analysis_model(file: ifcopenshell.file) -> ifcopenshell.entit
     A 3D analytical model is assumed.
 
     :return: The newly created IfcStructuralAnalysisModel
-    :rtype: ifcopenshell.entity_instance
 
     Example:
 

src/ifcopenshell-python/ifcopenshell/api/structural/add_structural_load.py

@@ -30,13 +30,10 @@ def add_structural_load(
     may be defined as a configuration of multiple loads.
 
     :param name: The name of the load
-    :type name: str,optional
     :param ifc_class: The subtype of IfcStructuralLoad to create. Consult
         the IFC documentation to see all the types of loads.
-    :type ifc_class: str
     :return: The newly created load entity, depending on the ifc_class
         specified.
-    :rtype: ifcopenshell.entity_instance
 
     Example:
 

src/ifcopenshell-python/ifcopenshell/api/structural/add_structural_load_case.py

@@ -25,16 +25,12 @@ def add_structural_load_case(
     """Adds a new load case, which is a collection of related load groups
 
     :param name: The name of the load case
-    :type name: str
     :param action_type: Choose from EXTRAORDINARY_A, PERMANENT_G,
         or VARIABLE_Q, taken from the Eurocode standard.
-    :type action_type: str
     :param action_source: The source of the load case, such as DEAD_LOAD_G,
         LIVE_LOAD_Q, TRANSPORT, ICE, etc. For the full list consult
         IfcActionSourceTypeEnum in the IFC documentation.
-    :type action_source: str
     :return: The new IfcStructuralLoadCase
-    :rtype: ifcopenshell.entity_instance
     """
 
     load_case = ifcopenshell.api.root.create_entity(

src/ifcopenshell-python/ifcopenshell/api/structural/add_structural_load_group.py

@@ -25,16 +25,12 @@ def add_structural_load_group(
     """Adds a new load group, which is a collection of related loads
 
     :param name: The name of the load group
-    :type name: str
     :param action_type: Choose from EXTRAORDINARY_A, PERMANENT_G,
         or VARIABLE_Q, taken from the Eurocode standard.
-    :type action_type: str
     :param action_source: The source of the load case, such as DEAD_LOAD_G,
         LIVE_LOAD_Q, TRANSPORT, ICE, etc. For the full list consult
         IfcActionSourceTypeEnum in the IFC documentation.
-    :type action_source: str
     :return: The new IfcStructuralLoadCase
-    :rtype: ifcopenshell.entity_instance
     """
 
     load_group = ifcopenshell.api.root.create_entity(