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/HttpManagerRestricted.hs

@@ -8,7 +8,6 @@
  -}
 
 {-# LANGUAGE ScopedTypeVariables, DeriveDataTypeable, LambdaCase, PatternGuards #-}
-{-# LANGUAGE CPP #-}
 
 module Utility.HttpManagerRestricted (
 	restrictManagerSettings,
@@ -30,9 +29,7 @@ import qualified Data.ByteString.UTF8 as BU
 import Data.Default
 import Data.Typeable
 import Control.Applicative
-#if MIN_VERSION_base(4,9,0)
 import qualified Data.Semigroup as Sem
-#endif
 import Data.Monoid
 import Prelude
 
@@ -51,17 +48,9 @@ instance Monoid Restriction where
 	mempty = Restriction
 		{ checkAddressRestriction = \_ -> Nothing
 		}
-#if MIN_VERSION_base(4,11,0)
-#elif MIN_VERSION_base(4,9,0)
-	mappend = (Sem.<>)
-#else
-	mappend = appendRestrictions
-#endif
 
-#if MIN_VERSION_base(4,9,0)
 instance Sem.Semigroup Restriction where
 	(<>) = appendRestrictions
-#endif
 
 -- | An exception used to indicate that the connection was restricted.
 data ConnectionRestricted = ConnectionRestricted String
@@ -93,11 +82,7 @@ restrictManagerSettings
 restrictManagerSettings cfg base = restrictProxy cfg $ base
 	{ managerRawConnection = restrictedRawConnection cfg
 	, managerTlsConnection = restrictedTlsConnection cfg
-#if MIN_VERSION_http_client(0,5,0)
 	, managerWrapException = wrapOurExceptions base
-#else
-	, managerWrapIOException = wrapOurExceptions base
-#endif
 	}
 
 restrictProxy
@@ -159,7 +144,6 @@ restrictProxy cfg base = do
 			, proxyPort = fromIntegral pn
 			}
 
-#if MIN_VERSION_http_client(0,5,0)
 wrapOurExceptions :: ManagerSettings -> Request -> IO a -> IO a
 wrapOurExceptions base req a =
 	let wrapper se
@@ -168,18 +152,6 @@ wrapOurExceptions base req a =
 				InternalException se
 		| otherwise = se
 	 in managerWrapException base req (handle (throwIO . wrapper) a)
-#else
-wrapOurExceptions :: ManagerSettings -> IO a -> IO a
-wrapOurExceptions base a =
-	let wrapper se = case fromException se of
-		Just (_ :: ConnectionRestricted) ->
-			-- Not really a TLS exception, but there is no
-			-- way to put SomeException in the 
-			-- InternalIOException this old version uses.
-			toException $ TlsException se
-		Nothing -> se
-	in managerWrapIOException base (handle (throwIO . wrapper) a)
-#endif
 
 restrictedRawConnection :: Restriction -> IO (Maybe HostAddress -> String -> Int -> IO Connection)
 restrictedRawConnection cfg = getConnection cfg Nothing