Remove direct dependency on elliptic-curve crate

Using the re-export from p256 ensures we always use the correct version.

Cargo.lock

@@ -47,7 +47,6 @@ dependencies = [
  "chrono",
  "console",
  "dialoguer",
- "elliptic-curve",
  "env_logger",
  "gumdrop",
  "hex",

Cargo.toml

@@ -17,7 +17,6 @@ bech32 = "0.8"
 chrono = "0.4"
 console = "0.14"
 dialoguer = "0.8"
-elliptic-curve = "0.8"
 env_logger = "0.8"
 gumdrop = "0.8"
 hex = "0.4"

src/p256.rs

@@ -1,5 +1,5 @@
 use bech32::{ToBase32, Variant};
-use elliptic_curve::sec1::{FromEncodedPoint, ToEncodedPoint};
+use p256::elliptic_curve::sec1::{FromEncodedPoint, ToEncodedPoint};
 use sha2::{Digest, Sha256};
 use std::convert::TryInto;
 use std::fmt;