Remove the X_OK define, it is unused.

Reviewed-by: NAndy Polyakov <appro@openssl.org>
Reviewed-by: NRichard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/4188)

apps/ca.c

@@ -38,7 +38,6 @@
 
 #ifndef W_OK
 # define F_OK 0
-# define X_OK 1
 # define W_OK 2
 # define R_OK 4
 #endif