simplify interface by removing size

Add size to the returned key after the fact, unless the remote happened
to add it itself.

Annex/Import.hs

@@ -391,7 +391,11 @@ importKeys remote importtreeconfig importcontent importablecontents = do
 			Nothing -> error "internal" -- checked earlier
 			Just a -> do
 				let importer p = do
-					k <- a loc cid sz p
+					unsizedk <- a loc cid p
+					-- This avoids every remote needing
+					-- to add the size.
+					let k = alterKey unsizedk $ \kd -> kd
+						{ keySize = keySize kd <|> Just sz }
 					checkSecureHashes k >>= \case
 						Nothing -> do
 							recordcidkey cidmap db cid k

Remote/Directory.hs

@@ -350,8 +350,8 @@ guardSameContentIdentifiers cont old new
 	| new == Just old = cont
 	| otherwise = giveup "file content has changed"
 
-importKeyM :: FilePath -> ExportLocation -> ContentIdentifier -> ByteSize -> MeterUpdate -> Annex Key
-importKeyM dir loc cid sz p = do
+importKeyM :: FilePath -> ExportLocation -> ContentIdentifier -> MeterUpdate -> Annex Key
+importKeyM dir loc cid p = do
 	backend <- chooseBackend (fromRawFilePath f)
 	k <- fst <$> genKey ks p backend
 	currcid <- liftIO $ mkContentIdentifier absf =<< getFileStatus absf

Types/Remote.hs

@@ -287,7 +287,7 @@ data ImportActions a = ImportActions
 	-- since the ContentIdentifier was generated.
 	--
 	-- Throws exception on failure.
-	, importKey :: Maybe (ExportLocation -> ContentIdentifier -> ByteSize -> MeterUpdate -> a Key)
+	, importKey :: Maybe (ExportLocation -> ContentIdentifier -> MeterUpdate -> a Key)
 	-- Retrieves a file from the remote. Ensures that the file
 	-- it retrieves has the requested ContentIdentifier.
 	--