Disable utmpx permanently

On Linux, utmpx and utmp are identical.  However, documentation (manual
pages) covers utmp, and just says about utmpx that it's identical to
utmp.  It seems that it's preferred to use utmp, at least by reading the
manual pages.

Moreover, we were defaulting to utmp (utmpx had to be explicitly enabled
at configuration time).  So, it seems safer to just make it permanent,
which should not affect default builds.

Signed-off-by: Alejandro Colomar <alx@kernel.org>

libmisc/failure.h

@@ -13,11 +13,7 @@
 
 #include "defines.h"
 #include "faillog.h"
-#ifdef USE_UTMPX
-#include <utmpx.h>
-#else					/* !USE_UTMPX */
 #include <utmp.h>
-#endif					/* !USE_UTMPX */
 
 /*
  * failure - make failure entry
@@ -51,11 +47,7 @@ extern void failprint (const struct faillog *);
  *	failtmp updates the (struct utmp) formatted failure log which
  *	maintains a record of all login failures.
  */
-#ifdef USE_UTMPX
-extern void failtmp (const char *username, const struct utmpx *);
-#else				/* !USE_UTMPX */
 extern void failtmp (const char *username, const struct utmp *);
-#endif				/* !USE_UTMPX */
 
 #endif