Fix SpringTestContext checkstyle

Issue: gh-5015

config/src/test/java/org/springframework/security/config/test/SpringTestContext.java

@@ -17,7 +17,6 @@
 package org.springframework.security.config.test;
 
 import org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor;
-import org.springframework.context.ApplicationContext;
 import org.springframework.context.ConfigurableApplicationContext;
 import org.springframework.mock.web.MockServletConfig;
 import org.springframework.mock.web.MockServletContext;