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. :^)

Userland/Libraries/LibCore/LocalSocket.cpp

@@ -26,6 +26,7 @@
 
 #include <LibCore/LocalSocket.h>
 #include <errno.h>
+#include <fcntl.h>
 #include <stdio.h>
 #include <sys/socket.h>
 #include <sys/stat.h>