Kernel: Remove SYS_OPEN

This can be done with SYS_OPENAT with fd set to AT_FDCWD

userspace/libraries/LibC/fcntl.cpp

@@ -15,7 +15,7 @@ int open(const char* path, int oflag, ...)
 	mode_t mode = va_arg(args, mode_t);
 	va_end(args);
 
-	return syscall(SYS_OPEN, path, oflag, __UMASKED_MODE(mode));
+	return openat(AT_FDCWD, path, oflag, mode);
 }
 
 int openat(int fd, const char* path, int oflag, ...)

userspace/libraries/LibC/include/sys/syscall.h

@@ -11,7 +11,6 @@ __BEGIN_DECLS
 	O(SYS_WRITE,			write)			\
 	O(SYS_TERMID,			termid)			\
 	O(SYS_CLOSE,			close)			\
-	O(SYS_OPEN,				open)			\
 	O(SYS_OPENAT,			openat)			\
 	O(SYS_SEEK,				seek)			\
 	O(SYS_TELL,				tell)			\