Remove unused imports (with newer protolude)

The changes here are from fixing stack build with LTS 15.8 (GHC 8.8.3)
to be warning-free. Most if not all come from the newer protolude
version, which adds some things like `unwords`.

So to make sure that we don't get unused import warnings with newer
stackage, this both raises the protolude lower bound and removes
these imports.

test/SpecHelper.hs

@@ -7,7 +7,6 @@ import qualified Data.Map.Strict        as M
 import qualified Data.Set               as S
 import qualified System.IO.Error        as E
 
-import Control.Monad        (void)
 import Data.Aeson           (Value (..), decode, encode)
 import Data.CaseInsensitive (CI (..))
 import Data.List            (lookup)