0024830: Remove redundant keyword 'mutable' in CDL declarations

Redundant keyword 'mutable' removed in CDL files.
In IGESConvGeom_GeomBuilder, unused methods MakeXY() and MakeXYZ() removed.
Method StepAP214_AutoDesignGroupAssignment::Init() replicating same method of the base class is removed as it causes CDL extraction error after above (seemingly irrelevant) changes.

src/StlMesh/StlMesh_Mesh.cdl

@@ -37,7 +37,7 @@ raises
 
 is
 
-    Create  returns mutable Mesh;
+    Create  returns Mesh;
     	---Purpose: Creates an empty mesh.
 
 

src/StlMesh/StlMesh_MeshDomain.cdl

@@ -32,12 +32,12 @@ raises
 
 is
 
-    Create  returns mutable MeshDomain;
+    Create  returns MeshDomain;
     	---Purpose: The mesh deflection is defaulted to Confusion from 
     	--          package Precision.
 
 
-    Create (Deflection : Real)  returns mutable MeshDomain
+    Create (Deflection : Real)  returns MeshDomain
     raises NegativeValue,
     	---Purpose: Raised if the deflection is lower than zero
     	   NullValue;

src/StlMesh/StlMesh_MeshTriangle.cdl

@@ -26,11 +26,11 @@ raises
 
 is
 
-    Create  returns mutable MeshTriangle;
+    Create  returns MeshTriangle;
     	---Purpose: empty constructor
 
 
-    Create (V1, V2, V3 : Integer; Xn, Yn, Zn : Real)  returns mutable MeshTriangle
+    Create (V1, V2, V3 : Integer; Xn, Yn, Zn : Real)  returns MeshTriangle
         ---Purpose: create a triangle defined with the indexes of its three vertices 
         --          and its orientation
     raises NegativeValue;