src: remove unused includes in string_bytes.h

PR-URL: #16606
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: XadillaX <admin@xcoder.in>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

src/string_bytes.h

@@ -27,9 +27,7 @@
 // Decodes a v8::Local<v8::String> or Buffer to a raw char*
 
 #include "v8.h"
-#include "node.h"
-#include "env-inl.h"
-#include "util.h"
+#include "env.h"
 
 namespace node {