* doc/org.texi (External links): Remove "file+emacs" and "file+sys"
syntax.
* lisp/org-compat.el (org): Support "file+emacs" and "file+sys" for the
time being.
* lisp/org-lint.el (org-lint--checkers): Add checker for obsolete link
types.
(org-lint-file-application): New function.
* lisp/org.el (org-link-parameters): Remove deprecated link types.