Remove VHDL driver extension/property after use.

* In CRL::vstDriver(), remove the Vhdl::EntityExtension right after driving
    the file. This avoid keeping in memory a mostly usnused structure and
    solve the "second write after modification" problem.

crlcore/src/ccore/alliance/vst/VstDriver.cpp

@@ -49,6 +49,8 @@ namespace CRL {
     vhdlEntity->toEntity( ccelltest );
     ccelltest << endl;
     ccelltest.close();
+
+    Vhdl::EntityExtension::destroy( cell );
   }