[BALL] Fix incorrect inheritance of PTE_ and Element Python bindings

PTE_ and Element are not derived from PropertyManager anymore since
0d47373. This prevents the BALLCore
module from being built using sip 4.19+ (partly fixes #606).

source/PYTHON/EXTENSIONS/BALL/PTE_.sip

@@ -9,7 +9,6 @@
 %End
 
 class Element
-  : PropertyManager
 {
 %TypeHeaderCode
 	#include <BALL/KERNEL/PTE.h>
@@ -65,7 +64,6 @@ class Element
  };
 
 class PTE_
-	: PropertyManager
 {
 	public:
 	PTE_();