Unconditionalize import fold'

Not exactly sure why it was conditionalized
but I kept running into an error and
'unconditionalizing' worked.

Author: Noir01

gibbon-compiler/src/Gibbon/HaskellFrontend.hs

@@ -8,8 +8,7 @@ module Gibbon.HaskellFrontend
 
 import           Control.Monad
 import           Data.Foldable ( foldrM )
-#if !MIN_VERSION_base(4,21,0)
-#endif
+import           Data.List (foldl')
 import           Data.Maybe (catMaybes, isJust)
 import qualified Data.Map as M
 import qualified Data.Set as S