ISO8601: Removed non-extended forms

- Removed support for non-extended forms, which is approximately half of the
  formats.  These include:
    YYYYMMDD
    YYYYWww
    YYYYWwwD
    hhmmѕsZ
    hhmmZ
    hhZ
  and combinations thereof. Essentially all forms that contains run-on sequences
  of integers, without separators. These removed forms will still be supported
  via rc.dateformat.
- Removed unsupported forms from iso8601d.t.cpp.
- Removed unsupported forms from datetime-negative.t, and corrected the tests
  that now succeed.

src/ISO8601.h

@@ -45,17 +45,11 @@ public:
 
 private:
   bool parse_date_time_ext (Nibbler&);
-  bool parse_date_time     (Nibbler&);
   bool parse_date_ext      (Nibbler&);
-  bool parse_date          (Nibbler&, bool);
   bool parse_off_ext       (Nibbler&);
-  bool parse_off           (Nibbler&);
   bool parse_time_ext      (Nibbler&);
-  bool parse_time          (Nibbler&, bool);
   bool parse_time_utc_ext  (Nibbler&);
-  bool parse_time_utc      (Nibbler&);
   bool parse_time_off_ext  (Nibbler&);
-  bool parse_time_off      (Nibbler&);
   int dayOfWeek (int, int, int);
   bool validate ();
   void resolve ();