remove useless liftetime paramenter in LoadBalance:: InstanceIter

[ethe]

Motivation

Because Loadbalance always get the discovery result like Arc<Vec<Instance>>, it should be 'static and does not need to give it a lifetime paramenter, it is useful to walkaround compiler issue rust-lang/rust#100013.

Solution

Modify service trait like this:

pub trait LoadBalance<D>: Send + Sync + 'static
where
    D: Discover,
{
    type InstanceIter: Iterator<Item = Address> + Send;
    type GetFut<'future>: Future<Output = Result<Self::InstanceIter, LoadBalanceError>>
        + Send
        + 'future
    where
        Self: 'future;
}