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/Feature/ConcurrentSpec.hs

@@ -5,7 +5,6 @@
 module Feature.ConcurrentSpec where
 
 import Control.Concurrent.Async (mapConcurrently)
-import Control.Monad            (void)
 import Network.Wai              (Application)
 
 import Control.Monad.Base