fix: remove unused import post-merge

Author: hstove

stacks-signer/src/v0/signer.rs

@@ -34,7 +34,6 @@ use libsigner::{BlockProposal, SignerEvent};
 use slog::{slog_debug, slog_error, slog_info, slog_warn};
 use stacks_common::types::chainstate::StacksAddress;
 use stacks_common::util::get_epoch_time_secs;
-use stacks_common::util::hash::Sha512Trunc256Sum;
 use stacks_common::util::secp256k1::MessageSignature;
 use stacks_common::{debug, error, info, warn};