Fix unused import in the ObjToMapTransformerTests

Author: artembilan

spring-integration-core/src/test/java/org/springframework/integration/transformer/ObjectToMapTransformerTests.java

@@ -19,7 +19,6 @@
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
 
-import java.io.IOException;
 import java.math.BigDecimal;
 import java.time.Instant;
 import java.util.ArrayList;