Remove support for 'e'/'c' as datetime pattern charactar

The meaning of 'u' was day number of week in SimpleDateFormat, it was changed to year in DateTimeFormatter. So we keep the old meaning of 'u' by substituting 'u' to 'e' internally and use DateTimeFormatter to parse the pattern string. In DateTimeFormatter, the 'e' and 'c' also represents day-of-week, we should mark them as illegal pattern character to stay the same as before.