Update log to jdk21 and delete dtt example files

src/main/java/de/hftstuttgart/dta/Testrunner.java

@@ -65,7 +65,7 @@ public class Testrunner
 
     public static void main(String[] args) throws Exception
     {
-        LOG.info("OpenJDK11 JUnit5/Jupiter Testrunner started");
+        LOG.info("OpenJDK21 JUnit5/Jupiter Testrunner started");
 
         LOG.info("initializing fields...");
         sourceFolders = args[0].split(":");

student.txt

-dtt::https://transfer.hft-stuttgart.de/gitlab/dtt/example_openjdk11-junit5-calculator-submission.git::none::none
\ No newline at end of file

teacher-dta.txt

-dtt::https://transfer.hft-stuttgart.de/gitlab/dtt/example_openjdk11-junit5-calculator-test.git::none::none::hftstuttgart/dta-jdk17-junit5-testrunner:latest