Enable duckduckgo by default

see https://github.com/searxng/searxng/pull/1219#discussion_r879543174

searx/settings.yml

@@ -480,7 +480,6 @@ engines:
   - name: duckduckgo
     engine: duckduckgo
     shortcut: ddg
-    disabled: true
 
   - name: duckduckgo images
     engine: duckduckgo_images