add testcase & remove unused code

src/test/java/com/alibaba/druid/bvt/sql/SQLCommentStatementTest.java

@@ -0,0 +1,23 @@
+package com.alibaba.druid.bvt.sql;
+
+import org.junit.Assert;
+
+import junit.framework.TestCase;
+
+import com.alibaba.druid.sql.ast.SQLStatement;
+import com.alibaba.druid.sql.parser.SQLStatementParser;
+import com.alibaba.druid.sql.test.TestUtils;
+
+public class SQLCommentStatementTest extends TestCase {
+
+    public void test_0() throws Exception {
+        String sql = "COMMENT on table t1 IS 'xxx'";
+
+        SQLStatementParser parser = new SQLStatementParser(sql);
+        SQLStatement stmt = parser.parseStatementList().get(0);
+
+        String text = TestUtils.outputSqlServer(stmt);
+
+        Assert.assertEquals("COMMENT ON TABLE t1 IS 'xxx'", text);
+    }
+}