hide the signature format switch where it doesn't make a difference

[chaserene]

coins where message signing is enabled display the Trezor/Electrum signature format switch. I'm unsure if it makes sense for non-Bitcoin coins with Electrum-fork wallets (Litecoin, Dash), but it's definitely meaningless for those without. e.g. for Ethereum the signature is the same even if I choose the Electrum format. I suggest removing the switch for coins where it doesn't make a difference.

How Sign & Verify works: https://trezor.io/guides/trezor-suite/trezor-suite-desktop/sign-and-verify-messages-trezor-suite