Don't transitively include <limits.h> from <sys/user.h>.

Bug: http://b/22735893
Change-Id: I27d0a1f7e2d477b8038e76bfc7fe05dd7e187344
diff --git a/libc/include/sys/user.h b/libc/include/sys/user.h
index 12af664..ce4c07c 100644
--- a/libc/include/sys/user.h
+++ b/libc/include/sys/user.h
@@ -30,7 +30,6 @@
 #define _SYS_USER_H_
 
 #include <sys/cdefs.h>
-#include <limits.h> /* For PAGE_SIZE. */
 #include <stddef.h> /* For size_t. */
 
 __BEGIN_DECLS