Revert the whole time zone mess

Revert the whole time zone mess

* lisp/org.el (org-time-string-to-time):
(org-time-string-to-seconds): Remove optional ZONE argument.
(org-2ft):
(org-check-before-date):
(org-check-after-date):
(org-check-dates-range):
(org-parse-time-string):
* lisp/org-clock.el (org-clock-get-sum-start):
(org-clock-out):
(org-clock-timestamps-change):
(org-clock-sum):
(org-clock-update-time-maybe):
* lisp/org-colview.el (org-columns--age-to-minutes): Apply change.
* testing/lisp/test-org-clock.el (org-test-clock-create-clock):
(test-org-clock/clocktable/scope):
* testing/lisp/test-org-colview.el (test-org-colview/columns-summary):
  Apply change.  Simplify tests to avoid daylight saving time issue.