Drop `PeerManager` type bound on `UtxoLookup` entirely

Drop `PeerManager` type bound on `UtxoLookup` entirely

In 67659677d4fdb6bf418d66dfa37c61706425232b we relaxed the bounds
set on `UtxoLookup` to enable those using `RoutingMessageHandler`
other than `P2PGossipSync` to use `UtxoLookup`. Sadly, because this
requires having a concrete `PeerManager` type which does *not* use
`UtxoLookup` in the `RoutingMessageHandler` type, this broke users
who were directly using `P2PGossipSync`.

We could split `UtxoLookup` into two, with different bounds, for
the two use-cases, but instead here we simply switch to storing a
reference to the `PeerManager` via a `dyn Fn` which allows us to
wake the `PeerManager` when we need to.

Fixes #2813