Remove references to dmalloc

There are more modern tools for memory debugging, get rid of DMALLOC
crap in the source code.

I've left one reference in backend.c to prevent a merge conflict but
this can be removed later.

src/util/mdb-tables.c

@@ -20,10 +20,6 @@
 
 #include "mdbtools.h"
 
-#ifdef DMALLOC
-#include "dmalloc.h"
-#endif
-
 struct type_struct {
 	char *name;
 	int value;