sim: cgen: require long long support

We require C11 now, so we can assume & require long long exists.
Drop this old code that hasn't been used for a long long time.

sim/common/cgen-utils.c

@@ -117,17 +117,6 @@ cgen_cpu_max_extra_bytes (void)
 
 #ifdef DI_FN_SUPPORT
 
-DI
-make_struct_di (hi, lo)
-     SI hi, lo;
-{
-  DI result;
-
-  result.hi = hi;
-  result.lo = lo;
-  return result;
-}
-
 DI
 ANDDI (a, b)
      DI a, b;