Move namespace declaration to header file

Change-Id: I5388d649ff3c8da0ff055f4aed6036647a123939
Reviewed-on: https://gerrit.libreoffice.org/40130Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Michael Stahl <mstahl@redhat.com>

xmlsecurity/inc/xsecctl.hxx

@@ -51,6 +51,7 @@
 #define NS_DC      "http://purl.org/dc/elements/1.1/"
 #define NS_XD      "http://uri.etsi.org/01903/v1.3.2#"
 #define NS_MDSSI   "http://schemas.openxmlformats.org/package/2006/digital-signature"
+#define NS_LOEXT   "urn:org:documentfoundation:names:experimental:office:xmlns:loext:1.0"
 
 #define ALGO_C14N          "http://www.w3.org/TR/2001/REC-xml-c14n-20010315"
 #define ALGO_RSASHA1       "http://www.w3.org/2000/09/xmldsig#rsa-sha1"

xmlsecurity/source/helper/xsecctl.cxx

@@ -727,8 +727,7 @@ void XSecController::exportSignature(
             if (!signatureInfo.ouGpgCertificate.isEmpty())
             {
                 pAttributeList = new SvXMLAttributeList();
-                pAttributeList->AddAttribute("xmlns:loext",
-                                             "urn:org:documentfoundation:names:experimental:office:xmlns:loext:1.0");
+                pAttributeList->AddAttribute("xmlns:loext", NS_LOEXT);
                 /* Write PGPData element */
                 xDocumentHandler->startElement(
                     "PGPData",