How can I remove page titles without removing the link in the navigation bar in twentyeleven?

You’ll need to remove the_title(); section from the following templates:

• content-aside.php
• content-featured.php
• content-gallery.php
• content-image.php
• content-intro.php
• content-link.php
• content-page.php
• content-quote.php
• content-single.php
• content-status.php
• content.php

Open the files and look for this:

<h2 class="entry-title">
  <a href="https://wordpress.stackexchange.com/questions/33038/<?php 
    the_permalink(); ?>" title="<?php printf( esc_attr__( 'Permalink to %s', 'twentyeleven' ), 
    the_title_attribute( 'echo=0' ) ); ?>" rel="bookmark">
  <?php the_title(); ?></a>
</h2>

The content will vary a little from template to template, just remove everything between the “entry-title” class to remove all titles from displaying in the pages.