remove many old version ifdefs

Drop support for building with ghc older than 8.4.4, and with older
versions of serveral haskell libraries than will be included in Debian 10.

The only remaining version ifdefs in the entire code base are now a couple
for aws!

This commit should only be merged after the Debian 10 release.
And perhaps it will need to wait longer than that; it would make
backporting new versions of  git-annex to Debian 9 (stretch) which
has been actively happening as recently as this year.

This commit was sponsored by Ilya Shlyakhter.

Utility/QuickCheck.hs

@@ -5,7 +5,6 @@
  - License: BSD-2-clause
  -}
 
-{-# LANGUAGE CPP #-}
 {-# OPTIONS_GHC -fno-warn-orphans #-}
 {-# LANGUAGE TypeSynonymInstances #-}
 
@@ -18,9 +17,7 @@ import Test.QuickCheck as X
 import Data.Time.Clock.POSIX
 import Data.Ratio
 import System.Posix.Types
-#if MIN_VERSION_QuickCheck(2,10,0)
 import Data.List.NonEmpty (NonEmpty(..))
-#endif
 import Prelude
 
 {- Times before the epoch are excluded. Half with decimal and half without. -}
@@ -45,11 +42,8 @@ instance Arbitrary FileID where
 instance Arbitrary FileOffset where
 	arbitrary = nonNegative arbitrarySizedIntegral
 
-{- Latest Quickcheck lacks this instance. -}
-#if MIN_VERSION_QuickCheck(2,10,0)
 instance Arbitrary l => Arbitrary (NonEmpty l) where
 	arbitrary = (:|) <$> arbitrary <*> arbitrary
-#endif
 
 nonNegative :: (Num a, Ord a) => Gen a -> Gen a
 nonNegative g = g `suchThat` (>= 0)