Remove dependency that isn't used yet (#9296)

Author: alex

src/rust/cryptography-x509-validation/Cargo.toml

@@ -10,6 +10,3 @@ rust-version = "1.56.0"
 [dependencies]
 asn1 = { version = "0.15.0", default-features = false }
 cryptography-x509 = { path = "../cryptography-x509" }
-
-[dev-dependencies]
-pem = "1.1"