ox-publish: Fix (invalid-read-syntax "#") error

* lisp/ox-publish.el (org-publish-find-title):
  Fix (invalid-read-syntax "#").

Since 8e1386cead0e4296f7bb063d07d64dd95ec0b231,
`org-element-interpret-data' no longer trims text properties attached
to strings.  We need to remove them before writing the title into the
cache, as text properties are not readable.

lisp/ox-publish.el

@@ -808,7 +808,8 @@ Default for SITEMAP-FILENAME is 'sitemap.org'."
        (org-mode)
        (let ((title
 	      (let ((property (plist-get (org-export-get-environment) :title)))
-		(if property (org-element-interpret-data property)
+		(if property
+		    (org-no-properties (org-element-interpret-data property))
 		  (file-name-nondirectory (file-name-sans-extension file))))))
 	 (unless visiting (kill-buffer buffer))
 	 (org-publish-cache-set-file-property file :title title)