in monobook.php change :
<h1 class="firstHeading"><?php $this->text('title') ?></h1>
into
<?php if($this->haveData('title') != wfMsgForContent('mainpage')){ ?>
<h1 class="firstHeading"><?php $this->text('title') ?></h1> <?php } ?>
How make this affects 'Main Page' and 'Main Page/Page 1', 'Main Page/Page 2', etc?