remove knovel (#3338)

Elsevier acquired Knovel in 2013

`data/knovel` has only one domain: `knovel.com`, and it's already in
`data/elsevier`

data/geolocation-!cn

@@ -85,7 +85,6 @@ include:embl
 include:freecodecamp
 include:kaggle
 include:khanacademy
-include:knovel
 include:laracasts
 include:libgen
 include:lifewire