[enh] move dictionaries, Erowid & IMDb out of general category

The general category is the category that is searched by default.
From a privacy standpoint it doesn't make sense to send all general
queries to specialized search engines that cannot deal with those
queries anyway.

searx/engines/duden.py

@@ -19,7 +19,7 @@ about = {
     "language": 'de',
 }
 
-categories = ['general', 'dictionaries']
+categories = ['dictionaries']
 paging = True
 
 # search-url

searx/engines/imdb.py

@@ -27,9 +27,7 @@ about = {
     "results": 'HTML',
 }
 
-categories = [
-    'general',
-]
+categories = []
 paging = False
 
 # suggestion_url = "https://sg.media-imdb.com/suggestion/{letter}/{query}.json"

searx/engines/sjp.py

@@ -21,7 +21,7 @@ about = {
     "language": 'pl',
 }
 
-categories = ['general', 'dictionaries']
+categories = ['dictionaries']
 paging = False
 
 URL = 'https://sjp.pwn.pl'

searx/engines/translated.py

@@ -14,7 +14,7 @@ about = {
 }
 
 engine_type = 'online_dictionary'
-categories = ['general', 'dictionaries']
+categories = ['dictionaries']
 url = 'https://api.mymemory.translated.net/get?q={query}&langpair={from_lang}|{to_lang}{key}'
 web_url = 'https://mymemory.translated.net/en/{from_lang}/{to_lang}/{query}'
 weight = 100