Upgrade to tracing 0.2.13

The primary motivation is to get the changes from
https://github.com/tokio-rs/tracing/pull/990. Example output:

```
$ RUSTDOC_LOG=debug rustdoc +rustc2
warning: some trace filter directives would enable traces that are disabled statically
 | `debug` would enable the DEBUG level for all targets
 = note: the static max level is `info`
 = help: to enable DEBUG logging, remove the `max_level_info` feature
```

- Remove useless test

  This was testing for an ICE when passing `RUST_LOG=rustc_middle`.  I
  noticed it because it started giving the tracing warning (because tests
  are not run with debug-logging enabled). Since this bug seems unlikely
  to re-occur, I just removed it altogether.

1 files changed, 0 insertions, 7 deletions

diff --git a/src/test/ui/issues/issue-18075.rs b/src/test/ui/issues/issue-18075.rs
deleted file mode 100644
index 56ec629c613..00000000000
--- a/src/test/ui/issues/issue-18075.rs
+++ /dev/null
@@ -1,7 +0,0 @@
-// run-pass
-// rustc-env:RUSTC_LOG=rustc::middle=debug
-
-fn main() {
-    let b = 1isize;
-    println!("{}", b);
-}