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/ExprIntrp/ExprIntrp_GenExp.cdl

@@ -31,7 +31,7 @@ is
     Create
     ---Purpose: Creates an empty generator
     ---Level: Advanced 
-    returns mutable GenExp is private;
+    returns GenExp is private;
 
     Create( myclass ) returns GenExp;
     

src/ExprIntrp/ExprIntrp_GenFct.cdl

@@ -30,7 +30,7 @@ is
 
     Create
     ---Level: Internal 
-    returns mutable GenFct is private;
+    returns GenFct is private;
 
     Create( myclass ) returns GenFct;
         

src/ExprIntrp/ExprIntrp_GenRel.cdl

@@ -29,7 +29,7 @@ is
     Create
     ---Purpose: Creates an empty generator
     ---Level: Advanced
-    returns mutable GenRel is private;
+    returns GenRel is private;
 
     Create( myclass ) returns GenRel;
     
@@ -49,7 +49,7 @@ is
     ---Purpose: Returns relation generated. Raises an exception if 
     --          IsDone answers false.
     ---Level: Advanced 
-    returns mutable GeneralRelation
+    returns GeneralRelation
     raises NoSuchObject
     is static;