Fix proxy extranonce range overflow after adding additional_coinbase_data

[Priceless-P]

Following this change , m.extranonce_size grew from 16 to 32 bytes. Proxy currently double-counted the prefix when calculating extranonce ranges, this now causes invalidExtranonceRange on channel creation.

This PR corrects the math by treating tproxy_e1_len as the actual end of range_1.

Currently we added the prefix twice:

let range_1 = prefix_len..prefix_len + tproxy_e1_len; // downstream extranonce1
let range_2 = prefix_len + tproxy_e1_len
    ..prefix_len + m.extranonce_size as usize;

With this change, we use tproxy_e1_len directly:

let range_1 = prefix_len..tproxy_e1_len // 16..27
let  range_2 = tproxy_e1_len..extranonce_size // 27..32

Also changed extranonce2_len in bridge.rs:
let extranonce2_len = m.extranonce_size - prefix_len

Now 

it works but I’m not sure if it is working the way we want .

Fixes https://github.com/demand-open-source/demand-pool/issues/264

Looking forward to your review @Fi3 @jbesraa

[Fi3]

since you are at it remove the proxy_extranonce1_len function that looks reduntant

[Priceless-P]

proxy_extranonce1_len is still used elsewhere
https://github.com/demand-open-source/demand-cli/blob/master/src/translator/upstream/upstream.rs#L533