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.

Database/Init.hs

@@ -5,8 +5,6 @@
  - Licensed under the GNU AGPL version 3 or higher.
  -}
 
-{-# LANGUAGE CPP #-}
-
 module Database.Init where
 
 import Annex.Common
@@ -16,11 +14,7 @@ import Utility.FileMode
 import Database.Persist.Sqlite
 import Control.Monad.IO.Class (liftIO)
 import qualified Data.Text as T
-#if MIN_VERSION_persistent_sqlite(2,6,2)
 import Lens.Micro
-#else
-import qualified Database.Sqlite as Sqlite
-#endif
 
 {- Ensures that the database is freshly initialized. Deletes any
  - existing database. Pass the migration action for the database.
@@ -38,12 +32,7 @@ initDb db migration = do
 	let tdb = T.pack tmpdb	
 	liftIO $ do
 		createDirectoryIfMissing True tmpdbdir
-#if MIN_VERSION_persistent_sqlite(2,6,2)
 		runSqliteInfo (enableWAL tdb) migration
-#else
-		enableWAL tdb
-		runSqlite tdb migration
-#endif
 	setAnnexDirPerm tmpdbdir
 	-- Work around sqlite bug that prevents it from honoring
 	-- less restrictive umasks.
@@ -61,16 +50,6 @@ initDb db migration = do
  -
  - Note that once WAL mode is enabled, it will persist whenever the
  - database is opened. -}
-#if MIN_VERSION_persistent_sqlite(2,6,2)
 enableWAL :: T.Text -> SqliteConnectionInfo
 enableWAL db = over walEnabled (const True) $ 
 	mkSqliteConnectionInfo db
-#else
-enableWAL :: T.Text -> IO ()
-enableWAL db = do
-	conn <- Sqlite.open db
-	stmt <- Sqlite.prepare conn (T.pack "PRAGMA journal_mode=WAL;")
-	void $ Sqlite.step stmt
-	void $ Sqlite.finalize stmt
-	Sqlite.close conn
-#endif