If you don't want the functionality provided by a tableselect element, the question has to be asked...why are you using a tableselect element?
It would make a lot more sense to use theme_table()
if you just want a bog standard HTML table:
$form['myfieldset']['mytable'] = array(
'#theme' => 'table',
'#header' => $header,
'#rows' => $rows
);