Fix references to non-existing or obsoleted man pages.

PR:	docs/51480 (only a small part)
Submitted by:	Diomidis D. Spinellis <dds@aueb.gr>

bin/ps/ps.1

@@ -301,9 +301,7 @@ the process has asked for random page replacement
 .Pf ( Dv MADV_RANDOM ,
 from
 .Xr madvise 2 ,
-for example,
-.Xr lisp 1
-in a garbage collect).
+for example, lisp in a garbage collect).
 .It E
 The process is trying to exit.
 .It L

bin/sh/sh.1

@@ -59,8 +59,7 @@ conform with the
 specification for the shell.  This version has many features which make
 it appear
 similar in some respects to the Korn shell, but it is not a Korn
-shell clone like
-.Xr pdksh 1 .
+shell clone like pdksh.
 Only features
 designated by POSIX, plus a few Berkeley extensions, are being
 incorporated into this shell.

usr.bin/ee/ee.1

@@ -368,7 +368,7 @@ One is by the traditional
 .Xr spell 1
 command, the other is with the
 optional
-.Xr ispell 1
+.Nm ispell
 command.
 .Pp
 Using

usr.bin/mt/mt.1

@@ -352,9 +352,7 @@ Extensions regarding the
 .Xr st 4
 driver appeared in
 .Bx 386 0.1
-as a separate
-.Xr st 1
-command, and have been merged into the
+as a separate st(1) command, and have been merged into the
 .Nm
 command in
 .Fx 2.1 .