v0.1.x lint fix, MSRV 1.28.0 updates (#1451)

* use dyn Trait syntax where appropriate

recent rust nightly started warning that not using `dyn` was
deprecated. This requires MSRV 1.27.0+.

* rustfmt fallout from dyn additions

* stop explicit allow of rust_2018_idioms

* more dyn Trait syntax

* drop tokio-macros from 0.1.x workspace

Since tokio-macros specifies an edition=2018, we would otherwise
require MSRV 1.31.0 to build/test it. And tokio-macros isn't used with
tokio 0.1.x.

* reactor: narrow tokio-io-pool dev dep to 0.1.4

Since 0.1.5-6 is now a edition=2018 crate, which has effective MSRV
1.31.0.

* narrow tempfile dev-dep to avoid MSRV bump

tempfile 3.1.0 pulls in rand 0.7.0 and is MSRV 1.32.0

* narrow flate2 dev-dep to avoid MSRV bump

flate2 1.0.10-11 have MSRV 1.34.0.

github refs: alexcrichton/flate2-rs#207

* fs: drop deprecated tempdir crate use in tests

In particular because it pulls in old rand duplicates. Replace use
with tempfile::tempdir() which has been available since tempfile
3.0.0.

backport-of: #1312

* increase CI MSRV to 1.28.0

tokio-executor/src/lib.rs

@@ -1,7 +1,5 @@
 #![deny(missing_docs, missing_debug_implementations, warnings)]
 #![doc(html_root_url = "https://docs.rs/tokio-executor/0.1.8")]
-// Our MSRV doesn't allow us to fix these warnings yet
-#![allow(rust_2018_idioms)]
 
 //! Task execution related traits and utilities.
 //!