correct sci-hub links/ add `.ru` and remove other 3rd party domains.

searx/settings.yml

@@ -2032,10 +2032,7 @@ doi_resolvers:
   doi.org: 'https://doi.org/'
   doai.io: 'https://dissem.in/'
   sci-hub.se: 'https://sci-hub.se/'
-  sci-hub.do: 'https://sci-hub.do/'
-  scihubtw.tw: 'https://scihubtw.tw/'
   sci-hub.st: 'https://sci-hub.st/'
-  sci-hub.bar: 'https://sci-hub.bar/'
-  sci-hub.it.nf: 'https://sci-hub.it.nf/'
+  sci-hub.ru: 'https://sci-hub.ru/'
 
 default_doi_resolver: 'oadoi.org'

tests/robot/settings_robot.yml

@@ -53,10 +53,7 @@ doi_resolvers:
   doi.org: 'https://doi.org/'
   doai.io: 'https://dissem.in/'
   sci-hub.se: 'https://sci-hub.se/'
-  sci-hub.do: 'https://sci-hub.do/'
-  scihubtw.tw: 'https://scihubtw.tw/'
   sci-hub.st: 'https://sci-hub.st/'
-  sci-hub.bar: 'https://sci-hub.bar/'
-  sci-hub.it.nf: 'https://sci-hub.it.nf/'
+  sci-hub.ru: 'https://sci-hub.ru/'
 
 default_doi_resolver: 'oadoi.org'