Remove unused import from the MessageDrivenAdapterTests

**Auto-cherry-pick to `7.0.x`**

Author: artembilan

spring-integration-kafka/src/test/java/org/springframework/integration/kafka/inbound/MessageDrivenAdapterTests.java

@@ -41,7 +41,6 @@
 import org.apache.kafka.common.header.internals.RecordHeaders;
 import org.assertj.core.api.InstanceOfAssertFactories;
 import org.junit.jupiter.api.Test;
-import org.junitpioneer.jupiter.RetryingTest;
 
 import org.springframework.core.retry.RetryListener;
 import org.springframework.core.retry.RetryPolicy;