Remove memory debugging/tracing support and all related options

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.

docs/x11/install.md

@@ -427,10 +427,6 @@ Troubleshooting                        {#x11_troubleshooting}
   argument functions, try putting the gcc fixinclude file paths early in the
   include path.
 
-- If you operator-related compile errors or strange memory problems
-  (for example in deletion of string arrays), set wxUSE_GLOBAL_MEMORY_OPERATORS
-  and wxUSE_MEMORY_TRACING to 0 in setup.h, and recompile.
-
 - If you get an internal compiler error in gcc, turn off optimisations.
 
 - Some compilers, such as Sun C++, may give a lot of warnings about