purify exportActions

Purifying exportActions will allow introspecting and modifying it,
which is needed to add progress bar display to it.

Only S3 and WebDAV ran an Annex action while constructing ExportActions.
There was a small performance gain from them doing that, since a
resource was able to be prepared and reused for multiple actions by
Command.Export.

As seen in commit 809cfbbd8a and
5d394023eb S3 and WebDAV actually create a
new handle for each access in normal, non-export use. It doesn't seem
worth making export use of them marginally more efficient than normal
use. It would be better to do that work upfront when constructing the
remote. Or perhaps use a MVar to cache a handle.

This commit was sponsored by Nick Piper on Patreon.

Remote/Directory.hs

@@ -63,7 +63,7 @@ gen r u c gc = do
 			, lockContent = Nothing
 			, checkPresent = checkPresentDummy
 			, checkPresentCheap = True
-			, exportActions = return $ ExportActions
+			, exportActions = ExportActions
 				{ storeExport = storeExportM dir
 				, retrieveExport = retrieveExportM dir
 				, removeExport = removeExportM dir