[xsl] Filter out elements that have one specific sub-element and nothing else

[stephan@xxxxxxxxxx]

Hi there,

I have an XML file like this:

<?xml version="1.0" encoding="UTF-8"?>
<funnylist>
    <listitem>
        <formatinfo color="yellow" />
        <stuffinside>Info</stuffinside> MoreInfo
    </listitem>
    <listitem>
        <formatinfo color="blue" />
    </listitem>
    <listitem>
        <formatinfo color="red" />EvenMoreInfo
    </listitem>
</funnylist>

I need to filter out this element:
    <listitem>
        <formatinfo color="blue" />
    </listitem>

The rule: if listitem contains only formatinfo and no other element or 
text then remove it.

I have no clue how to formulate the xPath.
Help appreciated.
:-) stw