Refactoring: Change sp_type_def_composite2::m_def from Spvar_definition* to Spvar_definition

Let's do the following change:

 class sp_type_def_composite2 : public sp_type_def

 {

-  Spvar_definition *m_def[2];

+  Spvar_definition m_def[2];

There's no a point to allocate Spvar_definition for m_def separately. They can reside inside sp_type_def_composite2 itself.

This will reduce the amount of pointers and will make the existing and the future code simpler.