Removed support for git versions older than 2.5.

This entirely removes Git.BuildVersion, which avoids the possibility that
git-annex will behave differently based on the version of git it was built
with, rather than the version it's used with.

Debian oldoldstable is the oldest version of git that git-annex needs to
support, since it's used in the amd64ancient build.

cabal configure will fail if the git version is too old.

Sponsored-by: Nicholas Golder-Manning

Git/CatFile.hs

@@ -54,7 +54,6 @@ import Git.Types
 import Git.HashObject
 import qualified Git.LsTree as LsTree
 import qualified Utility.CoProcess as CoProcess
-import qualified Git.BuildVersion as BuildVersion
 import Utility.Tuple
 
 data CatFileHandle = CatFileHandle 
@@ -403,14 +402,10 @@ withCatFileStream
 withCatFileStream check repo reader = assertLocal repo $
 	bracketIO start stop $ \(c, hin, hout, _) -> reader c hin hout
   where
-	params = catMaybes
-		[ Just $ Param "cat-file"
-		, Just $ Param ("--batch" ++ (if check then "-check" else "") ++ "=" ++ batchFormat)
-		-- This option makes it faster, but is not present in
-		-- older versions of git.
-		, if BuildVersion.older "2.4.3"
-			then Nothing
-			else Just $ Param "--buffer"
+	params =
+		[ Param "cat-file"
+		, Param ("--batch" ++ (if check then "-check" else "") ++ "=" ++ batchFormat)
+		, Param "--buffer" -- makes it faster
 		]
 
 	start = do