Revert "avoid rewriting SysConfig.hs with identical contents"

That made the Makefile want to rebuild the file each time if it's
dependencies were newer, as it was not updated.

Build/TestConfig.hs

@@ -5,7 +5,6 @@ module Build.TestConfig where
 import System.IO
 import System.Cmd
 import System.Exit
-import System.Directory
 
 type ConfigKey = String
 data ConfigValue =
@@ -37,14 +36,8 @@ instance Show Config where
 			valuetype (MaybeBoolConfig _) = "Maybe Bool"
 
 writeSysConfig :: [Config] -> IO ()
-writeSysConfig config = do
-	e <- doesFileExist dest
-	old <- if e then readFile dest else return []
-	if (old /= body)
-		then writeFile dest body
-		else return ()
+writeSysConfig config = writeFile "Build/SysConfig.hs" body
 	where
-		dest = "Build/SysConfig.hs"
 		body = unlines $ header ++ map show config ++ footer
 		header = [
 			  "{- Automatically generated. -}"