Why did changing my target framework from ".NET Framework 4 Client Profile" to ".NET framework 4" give me warning messages?

The line:

<startup>
    <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.0" />
</startup>

was added to my App.config file and now i get the warning messages:

Could not find schema information for the element 'supportedRuntime'

Could not find schema information for the attribute 'version'

Could not find schema information for the attribute 'sku'

Can I just delete that line from the config file? Everything works fine when I run the app.