[network] Remove reliance on discovery_set from config-generator
[network] Remove reliance on discovery_set from config-generator

This API is deprecated and should be read from storage. Now it is for Network.

Also cleaned up the redundancy in the API since this was largely a
dupication of ConfigBuilder

Closes: #3608
Approved by: zekun000

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