Remove old backward compatibility code

Remove old backward compatibility code

Once upon a time (< 2005) the CachedPixmaps directory was located
at ~/GNUstep/.AppInfo/ and that was later moved to
~/GNUstep/Library/WindowMaker. So Dan Pascu introduced this function
in 24519b62928fc29ae129a9522769922308fa414f to make the convertion
automatically to users back then.

As it is highly unlikely that there is an old-timer wmaker user still
running a pre-2005 wmaker which suddenly decides to switch to wmaker-crm
and runs into trouble with his CachedPixmaps folder, let's simply remove it
to make defaults.o 1.8% smaller (596 bytes).