Revert "post, memory test: add memory_post_test() to include file"

This reverts commit f18714dd61
which cuases compile errors on a number of boards.

Signed-off-by:  Wolfgang Denk <wd@denx.de>

include/post.h

@@ -187,7 +187,6 @@ extern int post_hotkeys_pressed(void);
 #define CONFIG_SYS_POST_CODEC		0x00200000
 #define CONFIG_SYS_POST_COPROC		0x00400000
 
-int memory_post_test(int flags);
 #endif /* CONFIG_POST */
 
 #endif /* _POST_H */