Remove updates text on plugin or themes list page

Add define('DISALLOW_FILE_MODS',true); to your wp-config.php file.

This will block users being able to use the plugin and theme
installation/update functionality from the WordPress admin area.
Setting this constant also disables the Plugin and Theme editor (i.e.
you don’t need to set DISALLOW_FILE_MODS and DISALLOW_FILE_EDIT, as on
it’s own DISALLOW_FILE_MODS will have the same effect).

http://codex.wordpress.org/Editing_wp-config.php#WordPress_Upgrade_Constants

The messages go away as well. I just tested it. Note: This also disable the file editor, which, in my opinion makes it doubleplusgood.