OZG-5217 [chore] adjust for java 21

Jenkinsfile

 pipeline {
     agent {
        node {
-           label 'ozgcloud-jenkins-build-agent'
+           label 'ozgcloud-jenkins-build-agent-21'
         }
     }
 

pom.xml

@@ -54,10 +54,6 @@
 	</modules>
 
 	<properties>
-		<java.version>21</java.version>
-		<maven.compiler.target>${java.version}</maven.compiler.target>
-		<maven.compiler.source>${java.version}</maven.compiler.source>
-
 		<vorgang-manager.version>2.4.0</vorgang-manager.version>
 
 		<jsoup.version>1.14.3</jsoup.version>