This same PowerShell could be used for any other list to remove all of the items. I just needed it to remove the OOB reusable content.
$siteColTemp = Get-SPSite "http://yourSiteCollectionUrl";
$reusableContentList = $siteColTemp.RootWeb.Lists["Reusable Content"];
$reusableContentItems = $reusableContentList.Items;
$reusableContentItemsCount = $reusableContentItems.Count;
for($x=$reusableContentItemsCount-1;$x -ge 0; $x--){
$reusableContentItems[$x].Delete();
}