add removeKey action to Remote

Not implemented for any remotes yet; probably the git remote is the only
one that will ever implement it.

Remote/GCrypt.hs

@@ -111,6 +111,7 @@ gen' r u c gc = do
 		, retrieveKeyFile = retreiveKeyFileDummy
 		, retrieveKeyFileCheap = \_ _ _ -> return False
 		, removeKey = removeKeyDummy
+		, lockContent = Nothing
 		, checkPresent = checkPresentDummy
 		, checkPresentCheap = repoCheap r
 		, whereisKey = Nothing