Remove useless use crate_name; imports.

A `crate_name::foo` path always works in 2018

components/profile/time.rs

@@ -26,7 +26,6 @@ use std::path::Path;
 use std::time::Duration;
 use std::{f64, thread, u32, u64};
 use time_crate::precise_time_ns;
-use tokio;
 use tokio::prelude::Future;
 
 pub trait Formattable {

components/profile/trace_dump.rs

@@ -5,7 +5,6 @@
 //! A module for writing time profiler traces out to a self contained HTML file.
 
 use profile_traits::time::{ProfilerCategory, TimerMetadata};
-use serde_json;
 use std::fs;
 use std::io::{self, Write};
 use std::path;