Remove left over references to QUOTE blocks
* lisp/org.el (org-quote-string): Remove variable.
(org-enable-fixed-width-editor, org-context): Update docstring.
(org-toggle-fixed-width-section): Remove function and binding.
(org-set-font-lock-defaults): Remove reference to `org-quote-string'.
* lisp/org-element.el (org-element-headline-parser,
org-element-headline-interpreter): Remove references to
`org-quote-string'.
* testing/lisp/test-org-element.el (test-org-element/headline-quote-keyword):
Remove test.
(test-org-element/headline-interpreter): Remove a test.