Loosen strict parsing requirement for desktop files

Loosen strict parsing requirement for desktop files

There are other desktop-looking files, for instance those having to do
with MIME typess, that would benefit from being able to be read by this
function.  It helps to have some flexibility.
* lisp/xdg.el (xdg-desktop-read-file): Remove an error condition.
* test/lisp/xdg-tests.el: Remove a test.