Drop disabled by default and pretty useless memory tracing code and all
the overlapping and poorly documented build options related to it.
Remove memory.cpp entirely and update all the make/project files, but
preserve the now completely trivial wx/memory.h for compatibility and
also keep including wx/string.h from wx/object.h as it seems like a lot
of existing code actually depends on this, even if it should not.
Replace the options in the propgrid sample with a couple of other
debug-related options that were not used before to avoid leaving the
"Debugging Section" completely empty.
