sweep: leave exclusive group unchanged on parameter update

Exclusive group is a static property that doesn't need to be updated.
Requiring the exclusive group to be passed into UpdateParams creates a
burden for the caller to make sure they supply the existing group.

This change will be beneficial for users that bump anchor sweeps that
have exclusive groups set.

lnrpc/walletrpc/walletkit_server.go

@@ -486,7 +486,7 @@ func (w *WalletKit) BumpFee(ctx context.Context,
 	// bump its fee, which will result in a replacement transaction (RBF)
 	// being broadcast. If it is not aware of the input however,
 	// lnwallet.ErrNotMine is returned.
-	params := sweep.Params{
+	params := sweep.ParamsUpdate{
 		Fee:   feePreference,
 		Force: in.Force,
 	}