Remove unused dependency

Author: tvdijen

composer.json

@@ -15,7 +15,6 @@
         "ext-spl": "*",
 
         "simplesamlphp/assert": "~1.8.1",
-        "simplesamlphp/composer-xmlprovider-installer": "~1.0.1",
         "simplesamlphp/saml2": "^5@dev",
         "simplesamlphp/xml-security": "~1.13.0",
         "simplesamlphp/xml-common": "~1.25.0"