RAMPART-454 Refresh stale POM comment about OpenSAML xacml-saml pin

The "Override stale 4.x transitive deps pulled by WSS4J 3.0.3" comment
predates both upgrades: we're on WSS4J 4.0.1 and OpenSAML 5.2.1 now.
Reword it to describe what the block actually does -- keep the xacml-saml
api/impl artifacts pinned to ${opensaml.version} so the whole OpenSAML
5.x set stays in lockstep regardless of what a transitive dependency
prefers.

Author: robertlazarski

pom.xml

@@ -557,7 +557,8 @@
                 <artifactId>opensaml-core-impl</artifactId>
                 <version>${opensaml.version}</version>
             </dependency>
-            <!-- Override stale 4.x transitive deps pulled by WSS4J 3.0.3 -->
+            <!-- Pin the OpenSAML xacml-saml artifacts to the same version
+                 as the rest of the OpenSAML 5.x set. -->
             <dependency>
                 <groupId>org.opensaml</groupId>
                 <artifactId>opensaml-xacml-saml-impl</artifactId>