remove not used import (#3309)

Author: lovepoem

dubbo-config/dubbo-config-spring/src/main/java/org/apache/dubbo/config/spring/ConfigCenterBean.java

@@ -16,7 +16,6 @@
  */
 package org.apache.dubbo.config.spring;
 
-import org.apache.dubbo.common.utils.CollectionUtils;
 import org.apache.dubbo.common.config.ConfigurationUtils;
 import org.apache.dubbo.common.utils.StringUtils;
 import org.apache.dubbo.config.ApplicationConfig;