use lookupKeyStaged in --batch code paths

Make --batch mode handle unstaged annexed files consistently whether the
file is unlocked or not. Before this, a unstaged locked file
would have the symlink on disk examined and operated on in --batch mode,
while an unstaged unlocked file would be skipped.

Note that, when not in batch mode, unstaged files are skipped over too.
That is actually somewhat new behavior; as late as 7.20191114 a
command like `git-annex whereis .` would operate on unstaged locked
files and skip over unstaged unlocked files. That changed during
optimisation of CmdLine.Seek with apparently little fanfare or notice.

Turns out that rmurl still behaved that way when given an unstaged file
on the command line. It was changed to use lookupKeyStaged to
handle its --batch mode. That also affected its non-batch mode, but
since that's just catching up to the change earlier made to most
other commands, I have not mentioed that in the changelog.

It may be that other uses of lookupKey should also change to
lookupKeyStaged. But it may also be that would slow down some things,
or lead to unwanted behavior changes, so I've kept the changes minimal
for now.

An example of a place where the use of lookupKey is better than
lookupKeyStaged is in Command.AddUrl, where it looks to see if the file
already exists, and adds the url to the file when so. It does not matter
there whether the file is staged or not (when it's locked). The use of
lookupKey in Command.Unused likewise seems good (and faster).

Sponsored-by: Nicholas Golder-Manning on Patreon

Command/RmUrl.hs

@@ -47,7 +47,7 @@ batchParser s = case separate (== ' ') (reverse s) of
 			return $ Right (f', reverse ru)
 
 start :: (SeekInput, (FilePath, URLString)) -> CommandStart
-start (si, (file, url)) = lookupKey file' >>= \case
+start (si, (file, url)) = lookupKeyStaged file' >>= \case
 	Nothing -> stop
 	Just key -> do
 		let ai = mkActionItem (key, AssociatedFile (Just file'))