Prohibit map and grep in void context

map and grep are not intended to be used as mutators, iterating
with side-effects should be done with for or foreach loops. This
fixes the one occurrence of the pattern, and bumps the perlcritic
policy to severity 5 for the map and grep policies.

Author: Dagfinn Ilmari Mannsåker <ilmari@ilmari.org>
Reviewed-by: Michael Paquier <michael@paquier.xyz>
Reviewed-by: Andrew Dunstan <andrew@dunslane.net>
Reviewed-by: Julien Rouhaud <rjuju123@gmail.com>
Discussion: https://postgr.es/m/87fsvzhhc4.fsf@wibble.ilmari.org

contrib/intarray/bench/create_test.pl

@@ -51,7 +51,7 @@ foreach my $i (1 .. 200000)
 	else
 	{
 		print $msg "$i\t{" . join(',', @sect) . "}\n";
-		map { print $map "$i\t$_\n" } @sect;
+		print $map "$i\t$_\n" foreach @sect;
 	}
 }
 close $map;