Reduce the block size also when only the legacy block prop is running

[rach-id]

Currently, we only reduce the block size when both reactors are running:

celestia-core/node/node.go

Lines 460 to 463 in 6f0700a

	if config.Consensus.EnableLegacyBlockProp {
	types.MaxBlockSizeBytes = types.ReducedMaxBlockSizeBytes // reduce the max block size to avoid overloading the legacy block prop mechanism
	propagator = propagation.NewNoOpPropagator()
	propagationReactor = nil

We should also cover the case where only the legacy block prop is running and not the propagation reactor