Remove chrono feature from tracing

Cargo.lock

@@ -5004,7 +5004,6 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "f7b33f8b2ef2ab0c3778c12646d9c42a24f7772bee4cdafc72199644a9f58fdc"
 dependencies = [
  "ansi_term 0.12.1",
- "chrono",
  "lazy_static",
  "matchers",
  "parking_lot 0.9.0",

src/librustc_driver/Cargo.toml

@@ -13,7 +13,7 @@ crate-type = ["dylib"]
 lazy_static = "1.0"
 libc = "0.2"
 log = { package = "tracing", version = "0.1.18", features = ["release_max_level_info"]  }
-tracing-subscriber = { version = "0.2.10", default-features = false, features = ["fmt", "env-filter", "smallvec", "parking_lot", "ansi", "chrono"] }
+tracing-subscriber = { version = "0.2.10", default-features = false, features = ["fmt", "env-filter", "smallvec", "parking_lot", "ansi"] }
 rustc_middle = { path = "../librustc_middle" }
 rustc_ast_pretty = { path = "../librustc_ast_pretty" }
 rustc_target = { path = "../librustc_target" }