LibC+Everywhere: Remove open_with_path_length() in favor of open()

This API was a mostly gratuitous deviation from POSIX that gave up some
portability in exchange for avoiding the occasional strlen().

I don't think that was actually achieving anything valuable, so let's
just chill out and have the same open() API as everyone else. :^)

AK/StackInfo.cpp

@@ -27,6 +27,7 @@
 #include <AK/Assertions.h>
 #include <AK/StackInfo.h>
 #include <stdio.h>
+#include <string.h>
 
 #ifdef __serenity__
 #    include <serenity.h>