Remove dependency on chrono (#515)

Author: viglia

sentry-types/Cargo.toml

@@ -30,4 +30,3 @@ thiserror = "1.0.15"
 time = { version = "0.3.5", features = ["formatting", "parsing"] }
 url = { version = "2.1.1", features = ["serde"] }
 uuid = { version = "1.0.0", features = ["v4", "serde"] }
-chrono = { version = "0.4.22",  features = ["serde"] }