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.

src/PostgREST/ApiRequest.hs

@@ -28,8 +28,8 @@ import qualified Data.Vector          as V
 
 import Control.Arrow             ((***))
 import Data.Aeson.Types          (emptyArray, emptyObject)
-import Data.List                 (elem, last, lookup, partition)
-import Data.List.NonEmpty        (NonEmpty, head)
+import Data.List                 (last, lookup, partition)
+import Data.List.NonEmpty        (head)
 import Data.Maybe                (fromJust)
 import Data.Ranged.Ranges        (Range (..), emptyRange,
                                   rangeIntersection)