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/QueryBuilder.hs

@@ -22,7 +22,7 @@ module PostgREST.QueryBuilder (
 
 import qualified Data.Set as S
 
-import Data.Text (intercalate, unwords)
+import Data.Text (intercalate)
 import Data.Tree (Tree (..))
 
 import Data.Maybe