doc/nethack.6: Fix invalid *roff syntax

Also fix a case hidden by a comment.

Fixes:
$ nroff -ww -z -man doc/*.[67]
troff:doc/nethack.6:68: warning: escape character ignored before '@'
troff:doc/nethack.6:292: warning: escape character ignored before '@'

doc/nethack.6

@@ -65,7 +65,7 @@ nethack \- Exploring The Mazes of Menace
 .I race
 ]
 [
-.B \-\@
+.B \-@
 ]
 .PP
 Also
@@ -240,7 +240,7 @@ character's gender.  Any of the parts of the suffix may be left out.
 can be used to determine the character profession, also known as the role.
 You can specify either the male or female name for the character role, or
 the first three characters of the role as an abbreviation.
-.\" .B "\-p \@"
+.\" .B "\-p @"
 .\" has been retained to explicitly request that a random role be chosen.
 .\" It may need to be quoted with a backslash (\\@) if @
 .\" is the "kill" character (see "stty") for the terminal, in order
@@ -289,7 +289,7 @@ is already used for the
 .I Rogue
 role.
 .PP
-.B \-\@
+.B \-@
 tells nethack to choose any omitted characteristics (profession/role, race,
 gender, alignment) randomly without prompting.
 Otherwise, leaving out any of these characteristics will result in you