avoid using MonadFail in ParseDuration

There's no instance for Either String, so that makes it not as useful as
it could be, so instead just return an Either String.

Types/GitConfig.hs

@@ -177,7 +177,7 @@ extractGitConfig configsource r = GitConfig
 	, annexFsckNudge = getbool (annexConfig "fscknudge") True
 	, annexAutoUpgrade = toAutoUpgrade $
 		getmaybe (annexConfig "autoupgrade")
-	, annexExpireUnused = maybe Nothing Just . parseDuration
+	, annexExpireUnused = either (const Nothing) Just . parseDuration
 		<$> getmaybe (annexConfig "expireunused")
 	, annexSecureEraseCommand = getmaybe (annexConfig "secure-erase-command")
 	, annexGenMetaData = getbool (annexConfig "genmetadata") False

Types/ScheduledActivity.hs

@@ -46,16 +46,15 @@ parseScheduledActivity :: String -> Either String ScheduledActivity
 parseScheduledActivity s = case words s of
 	("fsck":"self":d:rest) -> qualified $ ScheduledSelfFsck
 		<$> parseSchedule (unwords rest)
-		<*> getduration d
+		<*> parseDuration d
 	("fsck":u:d:rest) -> qualified $ ScheduledRemoteFsck
 		<$> pure (toUUID u)
 		<*> parseSchedule (unwords rest)
-		<*> getduration d
+		<*> parseDuration d
 	_ -> qualified $ Left "unknown activity"
   where
 	qualified (Left e) = Left $ e ++ " in \"" ++ s ++ "\""
 	qualified v = v
-	getduration d = maybe (Left $ "failed to parse duration \""++d++"\"") Right (parseDuration d)
 
 fromScheduledActivities :: [ScheduledActivity] -> String
 fromScheduledActivities = intercalate "; " . map fromScheduledActivity