Improve startup time for commands that do not operate on remotes

And for tab completion, by not unnessessarily statting paths to remotes,
which used to cause eg, spin-up of removable drives.

Got rid of the remotes member of Git.Repo. This was a bit painful.

Remote.Git modifies the list of remotes as it reads their configs,
so still need a persistent list of remotes. So, put it in as
Annex.gitremotes. It's only populated by getGitRemotes, so commands
like examinekey that don't care about remotes won't do so.

This commit was sponsored by Jake Vosloo on Patreon.

CmdLine/GitAnnex/Options.hs

@@ -1,6 +1,6 @@
 {- git-annex command-line option parsing
  -
- - Copyright 2010-2017 Joey Hess <id@joeyh.name>
+ - Copyright 2010-2018 Joey Hess <id@joeyh.name>
  -
  - Licensed under the GNU GPL version 3 or higher.
  -}
@@ -10,10 +10,12 @@ module CmdLine.GitAnnex.Options where
 import Options.Applicative
 import Options.Applicative.Builder.Internal
 import Control.Concurrent
+import qualified Data.Map as M
 
 import Annex.Common
 import qualified Git.Config
 import qualified Git.Construct
+import Git.Remote
 import Git.Types
 import Types.Key
 import Types.TrustLevel
@@ -348,9 +350,10 @@ completeRemotes :: HasCompleter f => Mod f a
 completeRemotes = completer $ mkCompleter $ \input -> do
 	r <- maybe (pure Nothing) (Just <$$> Git.Config.read)
 		=<< Git.Construct.fromCwd
-	return $ filter (input `isPrefixOf`) 
-		(maybe [] (mapMaybe remoteName . remotes) r)
-		
+	return $ filter (input `isPrefixOf`) $
+		map remoteKeyToRemoteName $
+			filter isRemoteKey $
+				maybe [] (M.keys . config) r
 		
 completeBackends :: HasCompleter f => Mod f a
 completeBackends = completeWith $