Fix math/rand create proc

[tadeohepperle]

The runtime.default_random_generator(&state) does nothing and should be removed. It is defined in base/runtime.random_generator.odin as

default_random_generator :: proc "contextless" (state: ^Default_Random_State = nil) -> Random_Generator {
	return {
		procedure = default_random_generator_proc,
		data = state,
	}
}

[gingerBill]

Why not just change this to make it useful?

[tadeohepperle]

Could you go into specifics? What would you like to have changed, to "make it useful"?