[mempool] removing unreachable
[mempool] removing unreachable

`inbound_network_task()` will panic if it ever receives an `Event` enum that is not listed.
As this list of event enums might grow, we should not panic here.

aptos-labs/aptos-core,aptos-labs/aptos-core,aptos-labs/aptos-core,libra/libra,libra/libra,libra/libra,aptos-labs/aptos-core,aptos-labs/aptos-core,aptos-labs/aptos-core,aptos-labs/aptos-core,libra/libra,libra/libra