Removed confnotify-6.0.patch.

I don't think it is a good idea to hardcode this patch in nixpkgs as it is likely that
a patch provided by a user will conflict with this patch. This is for instance the case
with the patch "single_tagset" (http://dwm.suckless.org/patches/single_tagset).
Merge pull request #1448 from pSub/dwm-remove-patch

Removed confnotify-6.0.patch.