Remove unused config.

skywalking-sniffer/skywalking-api/src/main/java/com/a/eye/skywalking/api/conf/Config.java

@@ -3,8 +3,6 @@ package com.a.eye.skywalking.api.conf;
 public class Config {
 
     public static class SkyWalking {
-        public static String USERNAME = "";
-
         public static String APPLICATION_CODE = "";
 
         public static boolean IS_PREMAIN_MODE = false;

skywalking-sniffer/skywalking-api/src/main/java/com/a/eye/skywalking/api/conf/SnifferConfigInitializer.java

@@ -33,10 +33,6 @@ public class SnifferConfigInitializer {
             }
         }
 
-        String username = System.getProperty("username");
-        if (!StringUtil.isEmpty(username)) {
-            Config.SkyWalking.USERNAME = username;
-        }
         String applicationCode = System.getProperty("applicationCode");
         if (!StringUtil.isEmpty(applicationCode)) {
             Config.SkyWalking.APPLICATION_CODE = applicationCode;
@@ -46,9 +42,6 @@ public class SnifferConfigInitializer {
             Config.SkyWalking.SERVERS = servers;
         }
 
-        if (StringUtil.isEmpty(Config.SkyWalking.USERNAME)) {
-            throw new ExceptionInInitializerError("'-Dusername=' is missing.");
-        }
         if (StringUtil.isEmpty(Config.SkyWalking.APPLICATION_CODE)) {
             throw new ExceptionInInitializerError("'-DapplicationCode=' is missing.");
         }