View file PF.Base/module/feed/install/version/4.5.1.xml.php

<upgrade>
    <settings>
        <setting>
            <group />
            <module_id>feed</module_id>
            <is_hidden>0</is_hidden>
            <type>drop</type>
            <var_name>top_stories_update</var_name>
            <phrase_var_name>setting_top_stories_update</phrase_var_name>
            <ordering>1</ordering>
            <version_id>4.5.1</version_id>
            <value><![CDATA[a:2:{s:7:"default";s:7:"comment";s:6:"values";a:3:{i:0;s:7:"comment";i:1;s:4:"like";i:2;s:4:"both";}}]]></value>
        </setting>
    </settings>
</upgrade>