various little fixes that should have been in earlier checkins

main.c

@@ -87,8 +87,6 @@ main0(void)
   cprintf("loaded userfs\n");
 
   scheduler();
-
-  return 0;
 }
 
 // Additional processors start here.

mp.c

 #include "types.h"
 #include "mp.h"
 #include "defs.h"
-#include "memlayout.h"
 #include "param.h"
 #include "x86.h"
 #include "traps.h"