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/dialect/oracle/parser/OracleExprParser.java

@@ -416,7 +416,7 @@ public class OracleExprParser extends SQLExprParser {
                     lexer.reset(mark_bp, mark_ch, Token.IDENTIFIER);
                     return expr;
                 }
-                accept(Token.ZONE);
+                acceptIdentifier("ZONE");
                 
                 SQLExpr timeZone = primary();
                 expr = new OracleDatetimeExpr(expr, timeZone);

src/main/java/com/alibaba/druid/sql/dialect/oracle/parser/OracleLexer.java

@@ -119,7 +119,6 @@ public class OracleLexer extends Lexer {
         map.put("SESSION", Token.SESSION);
         map.put("PROCEDURE", Token.PROCEDURE);
         map.put("LOCAL", Token.LOCAL);
-        map.put("ZONE", Token.ZONE);
         map.put("SYSDATE", Token.SYSDATE);
         map.put("DECLARE", Token.DECLARE);
         map.put("EXCEPTION", Token.EXCEPTION);

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"),