Replace secp256k1 with k256 crate

Rationale: we already have secp256k1 in our dependencies, as suggested
by Igor:
https://github.com/matter-labs/zksync-era/pull/2333#discussion_r1656531731

Cargo.lock

@@ -2308,6 +2308,25 @@ dependencies = [
  "zeroize",
 ]
 
+[[package]]
+name = "secp256k1"
+version = "0.29.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0e0cc0f1cf93f4969faf3ea1c7d8a9faed25918d96affa959720823dfe86d4f3"
+dependencies = [
+ "rand",
+ "secp256k1-sys",
+]
+
+[[package]]
+name = "secp256k1-sys"
+version = "0.10.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1433bd67156263443f14d603720b082dd3121779323fce20cba2aa07b874bc1b"
+dependencies = [
+ "cc",
+]
+
 [[package]]
 name = "semver"
 version = "1.0.23"
@@ -2538,8 +2557,8 @@ name = "tee-key-preexec"
 version = "0.1.2-alpha.1"
 dependencies = [
  "anyhow",
- "k256",
  "rand",
+ "secp256k1",
  "teepot",
  "tracing",
  "tracing-log",