Alpha/Endorser: bugfix

When removing old endorsments from the wallet (to avoid it growing),
only old endorsments were kept, or no endorsments at all were kept.

In addition, that function relied on the endorsments being sorted by
level.

src/proto_alpha/lib_delegate/client_baking_endorsement.ml

@@ -56,7 +56,7 @@ end = struct
             let rec remove_old acc = function
               | [] -> List.rev acc
               | ((_,lvl) as hd)::tl ->
-                  if Raw_level.diff new_lvl  lvl > 50l (*?*)  then
+                  if Raw_level.diff new_lvl lvl < 50l (*?*) then
                     remove_old (hd::acc) tl
                   else
                     List.rev acc