Remove <asm/page.h>.

If we have PAGE_SIZE/PAGESIZE, POSIX says they should be in <limits.h>.

Change-Id: I3c2d574ea2aea81f524874a156361411a4ffa18e
diff --git a/libc/include/sys/user.h b/libc/include/sys/user.h
index 90cce80..e16b1a5 100644
--- a/libc/include/sys/user.h
+++ b/libc/include/sys/user.h
@@ -30,6 +30,7 @@
 #define _SYS_USER_H_
 
 #include <sys/cdefs.h>
+#include <limits.h> /* For PAGE_SIZE. */
 
 __BEGIN_DECLS