MINOR: Remove call to Exit.exit() to prevent infinite recursion in Connect integration tests (#9015)

If we call org.apache.kafka.common.utils.Exit#exit(int code) with code=0, the current implementation will go into an infinite recursion and kill the VM with a stack overflow error. This happens only in integration tests because of the overrides of shutdown procedures and this commit addresses this issue by removing the redundant call to Exit#exit. 

Reviewers: Lucas Bradstreet <lucas@confluent.io>, Konstantine Karantasis <k.karantasis@gmail.com>, Chia-Ping Tsai <chia7712@gmail.com>

connect/runtime/src/test/java/org/apache/kafka/connect/util/clusters/EmbeddedConnectCluster.java

@@ -112,7 +112,6 @@ public class EmbeddedConnectCluster {
             log.warn(exitMessage);
             throw new UngracefulShutdownException(exitMessage);
         }
-        Exit.exit(0, message);
     };
 
     /**
@@ -124,7 +123,6 @@ public class EmbeddedConnectCluster {
             log.warn(haltMessage);
             throw new UngracefulShutdownException(haltMessage);
         }
-        Exit.halt(0, message);
     };
 
     /**