Clean up #includes

Remove unused headers, and avoid relying on transitive inclusions

`include-what-you-use` has been very useful for this!

include/asm/main.hpp

@@ -3,12 +3,9 @@
 #ifndef RGBDS_MAIN_H
 #define RGBDS_MAIN_H
 
-#include <stdint.h>
 #include <stdio.h>
 #include <string>
 
-#include "helpers.hpp"
-
 extern bool haltNop;
 extern bool warnOnHaltNop;
 extern bool optimizeLoads;