Revert "Add new trace segment for improving sampling performance."

This reverts commit 323468f056.

apm-commons/apm-trace/src/main/java/org/skywalking/apm/trace/AbstractTraceSegment.java

@@ -1,7 +0,0 @@
-package org.skywalking.apm.trace;
-
-/**
- * @author wusheng
- */
-public interface AbstractTraceSegment {
-}

apm-commons/apm-trace/src/main/java/org/skywalking/apm/trace/TraceSegment.java

@@ -19,7 +19,7 @@ import java.util.List;
  * <p>
  * Created by wusheng on 2017/2/17.
  */
-public class TraceSegment implements AbstractTraceSegment{
+public class TraceSegment {
     private static final String ID_TYPE = "Segment";
 
     /**

apm-commons/apm-trace/src/main/java/org/skywalking/apm/trace/UnsampleTraceSegment.java

@@ -1,7 +0,0 @@
-package org.skywalking.apm.trace;
-
-/**
- * @author wusheng
- */
-public class UnsampleTraceSegment {
-}