use types to enforce that removeAnnex can only be called inside lockContent

This fixed one bug where it needed to be and wasn't (in Assistant.Unused).
And also found one place where lockContent was used unnecessarily (by
drop --from remote).

A few other places like uninit probably don't really need to lockContent,
but it doesn't hurt to do call it anyway.

This commit was sponsored by David Wagner.

Command/Move.hs

@@ -91,7 +91,7 @@ expectedPresent dest key = do
 	return $ dest `elem` remotes
 
 toPerform :: Remote -> Bool -> Key -> AssociatedFile -> Bool -> Either String Bool -> CommandPerform
-toPerform dest move key afile fastcheck isthere = moveLock move key $
+toPerform dest move key afile fastcheck isthere = do
 	case isthere of
 		Left err -> do
 			showNote err
@@ -115,8 +115,8 @@ toPerform dest move key afile fastcheck isthere = moveLock move key $
 			finish
   where
 	finish
-		| move = do
-			removeAnnex key
+		| move = lockContent key $ \contentlock -> do
+			removeAnnex contentlock
 			next $ Command.Drop.cleanupLocal key
 		| otherwise = next $ return True
 
@@ -164,10 +164,3 @@ fromPerform src move key afile = ifM (inAnnex key)
 	dispatch True True = do -- finish moving
 		ok <- Remote.removeKey src key
 		next $ Command.Drop.cleanupRemote key src ok
-
-{- Locks a key in order for it to be moved away from the current repository.
- - No lock is needed when a key is being copied, or moved to the current
- - repository. -}
-moveLock :: Bool -> Key -> Annex a -> Annex a
-moveLock True key a = lockContent key a
-moveLock False _ a = a