ovpnmain.cgi: Remove unnecessary check/error message

ovpnmain.cgi: Remove unnecessary check/error message

This parameter can either be "host" or "net", but the existing check
only allows "net" entries. Since other entries are also valid but
don't require further action, this patch removes the error message.

Fixes: #12686
Signed-off-by: Leo-Andres Hofmann <hofmann@leo-andres.de>
Reviewed-by: Michael Tremer <michael.tremer@ipfire.org>
Signed-off-by: Arne Fitzenreiter <arne_f@ipfire.org>