multibit, fatbit: make _size build-time only

This commit makes mmbit_size() and fatbit_size compile-time only, and
adds a resource limit for very large multibits.

src/runtime.c

@@ -55,7 +55,6 @@
 #include "state.h"
 #include "ue2common.h"
 #include "util/exhaust.h"
-#include "util/fatbit.h"
 #include "util/multibit.h"
 
 static really_inline