enhancement #I5GS5F 优化Id生成器的Holder类的逻辑

liteflow-core/src/main/java/com/yomahub/liteflow/flow/id/IdGeneratorHolder.java

@@ -51,9 +51,4 @@ public class IdGeneratorHolder {
     public void setRequestIdGenerator(RequestIdGenerator requestIdGenerator) {
         this.requestIdGenerator = requestIdGenerator;
     }
-
-    public void clear(){
-        INSTANCE = null;
-    }
-
 }