More cleanups (outdated comments, extern crate statements etc)

README.md

@@ -184,7 +184,6 @@ Addition and subtraction is also supported.
 The following illustrates most supported operations to the date and time:
 
 ```rust
-
 use chrono::prelude::*;
 use chrono::Duration;
 

benches/chrono.rs

@@ -1,9 +1,6 @@
 //! Benchmarks for chrono that just depend on std
 #![cfg(feature = "__internal_bench")]
 
-extern crate chrono;
-extern crate criterion;
-
 use criterion::{black_box, criterion_group, criterion_main, BenchmarkId, Criterion};
 
 use chrono::prelude::*;

benches/serde.rs

@@ -1,8 +1,5 @@
 #![cfg(feature = "__internal_bench")]
 
-extern crate chrono;
-extern crate criterion;
-
 use criterion::{black_box, criterion_group, criterion_main, Criterion};
 
 use chrono::NaiveDateTime;