chore: remove rpc endpoints from networks.json

[bonustrack]

We should remove the rpc endpoints from networks.json

[ChaituVR]

We are blocked with this, snapshot-labs/snapshot-v1#3059

[ChaituVR]

Also should update how to add a new network
https://docs.snapshot.org/developer-guides/networks

[bonustrack]

We are blocked with this, snapshot-labs/snapshot#3059

For this, we can keep only rpcs node for the networks supported by SafeSnap and use free nodes there like cloudflare-eth.com