Remove unused import (MystenLabs#10450)

## Description 

Seeing warnings on latest `main`.

## Test Plan 

n/a

---
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skip the following section. Otherwise, please indicate what changed, and
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### Type of Change (Check all that apply)

- [ ] user-visible impact
- [ ] breaking change for a client SDKs
- [ ] breaking change for FNs (FN binary must upgrade)
- [ ] breaking change for validators or node operators (must upgrade
binaries)
- [ ] breaking change for on-chain data layout
- [ ] necessitate either a data wipe or data migration

### Release notes

external-crates/move/move-prover/interpreter/crypto/src/lib.rs

@@ -14,7 +14,7 @@
 
 use anyhow::{bail, Result};
 use ed25519_dalek::{
-    ed25519::signature::Signature, PublicKey as Ed25519PublicKey, Signature as Ed25519Signature,
+    PublicKey as Ed25519PublicKey, Signature as Ed25519Signature,
     PUBLIC_KEY_LENGTH as ED25519_PUBLIC_KEY_LENGTH, SIGNATURE_LENGTH as ED25519_SIGNATURE_LENGTH,
 };
 use sha2::{Digest, Sha256};