[ZCash] Switch to another zcash endpoint

[cypt4]

Description

lightwalletd was turned off so we need to switch our zcash grpc endpoint and block explorer url.
ECC team reccomended to use zec.rocks and https://3xpl.com/ instead.

Steps to reproduce

1. Try to retrieve zcash account balance
2. Try to check tx from history in block explorer

Actual result

Balance won't load, blockexplorer url won't load

Expected result

Everything is working

Reproduces how often

Easily reproduced

Brave version (brave://version info)

Every version that supports zcash

Channel information

• release (stable)
• beta
• nightly

Reproducibility

• with Brave Shields disabled
• with Brave Rewards disabled
• in the latest version of Chrome

Miscellaneous information

No response