do not override user's MDC

Author: 123liuziming

instrumentation/log4j/log4j-context-data/log4j-context-data-common/testing/src/main/java/io/opentelemetry/instrumentation/log4j/contextdata/Log4j2Test.java

@@ -7,10 +7,6 @@
 
 import static org.assertj.core.api.Assertions.assertThat;
 
-import io.opentelemetry.api.baggage.Baggage;
-import io.opentelemetry.api.trace.Span;
-import io.opentelemetry.context.Scope;
-import io.opentelemetry.instrumentation.api.incubator.log.LoggingContextConstants;
 import io.opentelemetry.instrumentation.testing.junit.InstrumentationExtension;
 import java.util.List;
 import java.util.concurrent.atomic.AtomicReference;