bug#25778: 25.1; [PATCH] Drastically simplify xdg-open check

[Vasilij Schneidermann <v.schneidermann@gmail.com>]

> As you can see from that above report, they don't show any signs of
> fixing it.

Well, fine.  I'm sorry for not noticing a five year old piece of code
that got mistakenly removed without anyone complaining.  What I don't
understand is why my patch (removing IMHO unnecessary DE detection) is
related to using nohup to work around a problem with xdg-open and
gnome-open/gvfs-open.  If you consider fixing the nohup problem a
prerequisite before this patch can be applied, OK, do that then, I can
wait until that's done and recommence discussion on the other issue.

That aside, I cannot reproduce any weird behavior, be it with or without
nohup and gvfs-open.  Both `(call-process "gvfs-open" nil 0 nil
"foo.pdf")` and `(call-process "nohup" nil 0 nil "gvfs-open"
"foo.pdf")` spawn my PDF reader successfully and don't do anything weird
after closing it.  Same if I pass "http://ix.de/" as last argument.  I
therefore consider the nohup issue a case of cargo-culting and would
like to drop its discussion entirely as it does not help with the
current issue.