Polish Imports in SpringTestRule

Fixes: gh-5001

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

@@ -19,7 +19,6 @@ package org.springframework.security.config.test;
 import org.junit.rules.MethodRule;
 import org.junit.runners.model.FrameworkMethod;
 import org.junit.runners.model.Statement;
-import org.springframework.security.core.context.SecurityContextHolder;
 import org.springframework.security.test.context.TestSecurityContextHolder;
 
 /**