Move functions operating on timestamp objects into org.el
* contrib/lisp/org-export.el (org-export-timestamp-has-time-p,
org-export-format-timestamp, org-export-split-timestamp-range,
org-export-translate-timestamp): Removed functions.
* lisp/org.el (org-timestamp-has-time-p, org-timestamp-format,
org-timestamp-split-range, org-timestamp-translate): New functions.
* contrib/lisp/org-e-ascii.el (org-e-ascii-timestamp): Apply move.
* contrib/lisp/org-e-groff.el (org-e-groff-timestamp): Apply move.
* contrib/lisp/org-e-html.el (org-e-html-timestamp): Apply move.
* contrib/lisp/org-e-latex.el (org-e-latex-timestamp): Apply move.
* contrib/lisp/org-e-odt.el (org-e-odt--format-timestamp,
org-e-odt-timestamp): Apply move.
* contrib/lisp/org-e-texinfo.el (org-e-texinfo-timestamp): Apply move.
* testing/lisp/test-org-export.el: Remove tests.
* testing/lisp/test-org.el: Add tests.