fix: remove empty RefreshTokens

Signed-off-by: m.nabokikh <maksim.nabokikh@flant.com>

server/api.go

@@ -291,9 +291,7 @@ func (d dexAPI) ListRefresh(ctx context.Context, req *api.ListRefreshReq) (*api.
 		if err == storage.ErrNotFound {
 			// This means that this user-client pair does not have a refresh token yet.
 			// An empty list should be returned instead of an error.
-			return &api.ListRefreshResp{
-				RefreshTokens: nil,
-			}, nil
+			return &api.ListRefreshResp{}, nil
 		}
 		d.logger.Errorf("api: failed to list refresh tokens %t here : %v", err == storage.ErrNotFound, err)
 		return nil, err