GCC reports many "deleting void* is undefined" warnings in
module TKOpenGl. This commit fixes them by using free() instead
of the delete operator generated by macro IMPLEMENT_MEMORY_OPERATORS.
This macro is defined in InterfaceGraphic_telem.hxx, the delete
operator provided is simply a wrapper around free(). So using free()
does the trick for those warnings.
Contributed by: Hugues Delorme