ssh: remove duplicate setting of MAIL env var

We already set it earlier in do_setup_env().

Fixes:		19261079 ("openssh: update to OpenSSH v8.7p1")
MFC after:	1 week
Sponsored by:	The FreeBSD Foundation

(cherry picked from commit 19780592)

crypto/openssh/session.c

@@ -1078,12 +1078,6 @@ do_setup_env(struct ssh *ssh, Session *s, const char *shell)
 # endif /* HAVE_CYGWIN */
 #endif /* HAVE_LOGIN_CAP */
 
-	if (!options.use_pam) {
-		snprintf(buf, sizeof buf, "%.200s/%.50s",
-		    _PATH_MAILDIR, pw->pw_name);
-		child_set_env(&env, &envsize, "MAIL", buf);
-	}
-
 	/* Normal systems set SHELL by default. */
 	child_set_env(&env, &envsize, "SHELL", shell);