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/Private/QueryFragment.hs

@@ -11,7 +11,7 @@ import qualified Data.HashMap.Strict           as HM
 import           Data.Maybe
 import           Data.Text                     (intercalate,
                                                 isInfixOf, replace,
-                                                toLower, unwords)
+                                                toLower)
 import qualified Data.Text                     as T (map, null,
                                                      takeWhile)
 import           PostgREST.Types