Removed unused import

Author: artembilan

spring-integration-file/src/test/java/org/springframework/integration/file/splitter/FileSplitterTests.java

@@ -37,7 +37,6 @@
 import org.junit.jupiter.api.BeforeAll;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.io.TempDir;
-import org.mockito.Mockito;
 
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.context.annotation.Bean;