Remove unncessary call remove_from_peers_set (#4742)

... this is superfluous because set_reserved_peers implementation
already calls this method here:

https://github.com/paritytech/polkadot-sdk/blob/cdb297b1

/substrate/client/network/src/protocol_controller.rs#L571,
so the call just ends producing this warnings whenever we manipulate the
peers set.

```
Trying to remove unknown reserved node 12D3KooWRCePWvHoBbz9PSkw4aogtdVqkVDhiwpcHZCqh4hdPTXC from SetId(3)
peerset warnings (from different peers)
```

Signed-off-by: Alexandru Gheorghe <alexandru.gheorghe@parity.io>