Remove conditional include of alloca.h, we don't define HAVE_ALLOCA_H.

The configure check for alloca() was removed long ago but this got
missed.

plugins/sudoers/gram.h

@@ -171,7 +171,7 @@ extern int sudoersdebug;
 #if ! defined YYSTYPE && ! defined YYSTYPE_IS_DECLARED
 union YYSTYPE
 {
-#line 88 "gram.y"
+#line 85 "gram.y"
 
     struct cmndspec *cmndspec;
     struct defaults *defaults;

plugins/sudoers/gram.y

@@ -29,9 +29,6 @@
 #include <stddef.h>
 #include <string.h>
 #include <unistd.h>
-#if defined(YYBISON) && defined(HAVE_ALLOCA_H) && !defined(__GNUC__)
-# include <alloca.h>
-#endif /* YYBISON && HAVE_ALLOCA_H && !__GNUC__ */
 #include <errno.h>
 
 #include "sudoers.h"