Remove dead engines from config.

I didn't remove the engines files because it always could be helpful if they come back.

searx/settings.yml

 #    shortcut : fa
 #    api_key : 'apikey' # required!
 
-# down - website is under criminal investigation by the UK
-#  - name : filecrop
-#    engine : filecrop
-#    categories : files
-#    shortcut : fc
-
   - name : 500px
     engine : www500px
     shortcut : px
 # Or you can use the html non-stable engine, activated by default
     engine : flickr_noapi
 
-  - name : general-file
-    engine : generalfile
-    shortcut : gf
-    disabled : True
-
   - name : gigablast
     engine : gigablast
     shortcut : gb