In r289137 the legacy_aliases compatibility shims for ata were removed,

also remove a leftover define used for implementing them.

Reviewed by:	mav
Differential Revision:	https://reviews.freebsd.org/D6726

sys/cam/ata/ata_da.c

@@ -774,10 +774,6 @@ static void		adashutdown(void *arg, int howto);
 static void		adasuspend(void *arg);
 static void		adaresume(void *arg);
 
-#ifndef	ADA_DEFAULT_LEGACY_ALIASES
-#define	ADA_DEFAULT_LEGACY_ALIASES	1
-#endif
-
 #ifndef ADA_DEFAULT_TIMEOUT
 #define ADA_DEFAULT_TIMEOUT 30	/* Timeout in seconds */
 #endif