Use Tor for ledger proxy instead of PIA

[tildelowengrimm]

Once we have Tor working, we should consider using it for the ledger proxy, rather than PIA.

If Brave is connecting to a ledger service over Tor, we should probably configure that as an onion service on our end. Should we use a single onion service rather than a full hidden service? We should consider using something like Alec Muffett's Enterprise Onion Toolkit on the infrastructure side.

[diracdeltas]

Setting a milestone, per discussion in Slack ledger channel, for using Tor instead of PIA. (not for running ledger as an onion service)

https://github.com/brave/internal/issues/298

[alexwykoff]

@flamsmark please migrate this issue to Brave core repos as needed

[tildelowengrimm]

This is probably brave/brave-browser#804 now.