Remove ant xgboost (#794)

* remove ant-xgboost code base

* update design doc

* fix analyze codegen

Author: Yancey0623

doc/ant-xgboost_design.md

@@ -1,5 +1,7 @@
 # _Design:_ ant-xgboost on sqlflow
 
+**NOTE: ant-xgboost on SQLFlow has moved to [backup_antxgboot_work branch](https://github.com/sql-machine-learning/sqlflow/tree/backup_antxgboost_work)**
+
 ## Overview
 
 This is a design doc about why and how to support running ant-xgboost via sqlflow as a machine learning estimator.

doc/ant-xgboost_user_guide.md

@@ -85,7 +85,7 @@ func genAnalyzer(pr *extendedSelect, db *DB, cwd, modelDir string) (*bytes.Buffe
 	if err != nil {
 		return nil, fmt.Errorf("loadModelMeta %v", err)
 	}
-	if !strings.HasPrefix(strings.ToUpper(pr.estimator), `XGB.`) {
+	if !strings.HasPrefix(strings.ToUpper(pr.estimator), `XGBOOST.`) {
 		return nil, fmt.Errorf("analyzer: model[%s] not supported", pr.estimator)
 	}
 	// We untar the XGBoost.{pr.trainedModel}.tar.gz and get three files.