refactor

Conflicts:
	src/main/java/com/alibaba/druid/sql/dialect/oracle/parser/OracleLexer.java
	src/main/java/com/alibaba/druid/sql/parser/SQLExprParser.java
	src/main/java/com/alibaba/druid/sql/parser/Token.java

src/main/java/com/alibaba/druid/sql/parser/SQLExprParser.java

@@ -217,7 +217,6 @@ public class SQLExprParser extends SQLParser {
             case REFERENCE:
             case KEY:
             case DISTINCT:
-            case ZONE:
             case LIMIT:
             case SCHEMA:
             case COLUMN:

src/main/java/com/alibaba/druid/sql/parser/Token.java

@@ -156,7 +156,6 @@ public enum Token {
     SESSION("SESSION"),
     PROCEDURE("PROCEDURE"),
     LOCAL("LOCAL"),
-    ZONE("ZONE"),
     SYSDATE("SYSDATE"),
     DECLARE("DECLARE"),
     EXCEPTION("EXCEPTION"),