Dead assert for !Send data in run conditions

I want to note that this assert currently does nothing, since a system's "send-ness" only gets set when it's initialized. This assert never gets triggered, so instead a panic occurs later on when the system actually tries to access a `NonSend` resource from the wrong thread. I'm not sure what the best solution to this is, but it's probably worth opening an issue about it.

_Originally posted by @JoJoJet in https://github.com/bevyengine/bevy/pull/7841#discussion_r1119537179_