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;

include/asm/warning.hpp

@@ -3,8 +3,6 @@
 #ifndef WARNING_H
 #define WARNING_H
 
-#include "helpers.hpp"
-
 extern unsigned int nbErrors, maxErrors;
 
 enum WarningState { WARNING_DEFAULT, WARNING_DISABLED, WARNING_ENABLED, WARNING_ERROR };