If, for whatever reason, you need to remove an entry from the magento admin menu, you have two simple options. Remove it using css, or alternatively, drop the following into a custom module's adminhtml.xml.
<?xml version="1.0"?>
<!-- Disable Catalog Price Rules Menu Entry -->
<config>
<menu>
<promo translate="title" module="catalogrule">
<children>
<catalog translate="title" module="catalogrule">
<depends>
<module>Disable_This_Module</module>
</depends>
</catalog>
</children>
</promo>
</menu>
</config>This overrides the core code pool's adminhtml definition, and puts a dependency on a non-existent module. Effectively, this disabled the menu item because it no longer meets the defined dependency requirements.
As always with any magento configuration / module changes, you may need to clear caches for this to take effect.