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/StepBasic/StepBasic_Effectivity.cdl

@@ -21,7 +21,7 @@ uses
 
 is
 
-    Create returns mutable Effectivity;
+    Create returns Effectivity;
 
     Init (me : mutable; aid : HAsciiString);