ps(1): Remove internal documentation for '-A'

Now that it is officially documented in the manual page.

Reviewed by:    kib
MFC after:      3 days
Sponsored by:   The FreeBSD Foundation
Differential Revision:  https://reviews.freebsd.org/D49606

(cherry picked from commit 8a3e58ed61)

bin/ps/ps.c

@@ -247,11 +247,6 @@ main(int argc, char *argv[])
 	while ((ch = getopt(argc, argv, PS_ARGS)) != -1)
 		switch (ch) {
 		case 'A':
-			/*
-			 * Exactly the same as `-ax'.   This has been
-			 * added for compatibility with SUSv3, but for
-			 * now it will not be described in the man page.
-			 */
 			all = xkeep = 1;
 			break;
 		case 'a':