Remove new desktop_clean needles again

These are no use :/ The Rawhide default background is a 'changes
with the time of day' one, and with the transparent top bar,
that makes a proper needle match impossible to reliably achieve,
as there is not a single pixel of the 'clean desktop' which
will always be the same any more. We'll have to come up with
something else. I'm trying out the use of an OCR match now.

needles/gnome/desktop_clean-20170616.json

@@ -1,25 +0,0 @@
-{
-  "properties": [],
-  "area": [
-    {
-      "type": "match",
-      "width": 67,
-      "xpos": 9,
-      "height": 15,
-      "ypos": 7
-    },
-    {
-      "type": "match",
-      "xpos": 970,
-      "width": 43,
-      "height": 18,
-      "ypos": 4
-    }
-  ],
-  "tags": [
-    "DESKTOP-gnome",
-    "ENV-DISTRI-fedora",
-    "LANGUAGE-english",
-    "graphical_desktop_clean"
-  ]
-}

needles/gnome/desktop_clean-20170616b.json

@@ -1,25 +0,0 @@
-{
-  "tags": [
-    "DESKTOP-gnome",
-    "ENV-DISTRI-fedora",
-    "LANGUAGE-english",
-    "graphical_desktop_clean"
-  ],
-  "properties": [],
-  "area": [
-    {
-      "ypos": 6,
-      "height": 15,
-      "width": 67,
-      "xpos": 9,
-      "type": "match"
-    },
-    {
-      "type": "match",
-      "width": 43,
-      "xpos": 970,
-      "height": 18,
-      "ypos": 4
-    }
-  ]
-}