Remove unused source memory.[ch]pp.

I could not find any references to this source file from any
other, and it looks like it has been largely unmodified for the
past 5 years. This suggests that it has been orphaned.

Author: zerebubuth

include/mapnik/memory.hpp

@@ -192,7 +192,6 @@ def ldconfig(*args,**kwargs):
     layer.cpp
     map.cpp
     load_map.cpp
-    memory.cpp
     palette.cpp
     marker_helpers.cpp
     transform_expression_grammar.cpp