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/Parsers.hs

@@ -9,10 +9,8 @@ module PostgREST.Parsers where
 import qualified Data.HashMap.Strict as M
 import qualified Data.Set            as S
 
-import Control.Monad           ((>>))
 import Data.Either.Combinators (mapLeft)
 import Data.Foldable           (foldl1)
-import Data.Functor            (($>))
 import Data.List               (init, last)
 import Data.Text               (intercalate, replace, strip)
 import Text.Read               (read)