Back out check_future_5 testing that errorURL is a URL

See ukf/ukf-meta#178 for details

mdx/_rules/check_future_5.xsl

@@ -13,7 +13,6 @@
     xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
     xmlns:md="urn:oasis:names:tc:SAML:2.0:metadata"
     xmlns:mdui="urn:oasis:names:tc:SAML:metadata:ui"
-    xmlns:mdxURL="xalan://uk.ac.sdss.xalan.md.URLchecker"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xmlns:idpdisc="urn:oasis:names:tc:SAML:profiles:SSO:idp-discovery-protocol"
     xmlns:set="http://exslt.org/sets"
@@ -24,16 +23,4 @@
     -->
     <xsl:import href="check_framework.xsl"/>
 
-    <xsl:template match="md:IDPSSODescriptor/@errorURL[mdxURL:invalidURL(.)]">
-        <xsl:call-template name="error">
-            <xsl:with-param name="m">
-                <xsl:value-of select='local-name()'/>
-                <xsl:text> '</xsl:text>
-                <xsl:value-of select="."/>
-                <xsl:text>' is not a valid URL: </xsl:text>
-                <xsl:value-of select="mdxURL:whyInvalid(.)"/>
-            </xsl:with-param>
-        </xsl:call-template>
-    </xsl:template>
-
 </xsl:stylesheet>