[tempdir] Remove deprecated tempdir

This removes the explicit dependency on tempdir, which has been
deprecated.

https://github.com/rust-lang-deprecated/tempdir#deprecation-note

The actual vendored crate hasn't been removed yet because tempdir is
being used by the "multipart" crate.

Change-Id: I081d2def8399ae1b7064ab3e797f67693be553c8
diff --git a/rustc_deps/Cargo.lock b/rustc_deps/Cargo.lock
index 90600e4..fcca920 100644
--- a/rustc_deps/Cargo.lock
+++ b/rustc_deps/Cargo.lock
@@ -409,7 +409,6 @@
  "serde_json 1.0.32 (registry+https://github.com/rust-lang/crates.io-index)",
  "slab 0.4.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "structopt 0.2.12 (registry+https://github.com/rust-lang/crates.io-index)",
- "tempdir 0.3.7 (registry+https://github.com/rust-lang/crates.io-index)",
  "tempfile 3.0.4 (registry+https://github.com/rust-lang/crates.io-index)",
  "time 0.1.40 (registry+https://github.com/rust-lang/crates.io-index)",
  "timebomb 0.1.2 (registry+https://github.com/rust-lang/crates.io-index)",
diff --git a/rustc_deps/Cargo.toml b/rustc_deps/Cargo.toml
index 1a1bc66..909c494 100644
--- a/rustc_deps/Cargo.toml
+++ b/rustc_deps/Cargo.toml
@@ -45,7 +45,6 @@
 serde_json = "1"
 slab = "0.4"
 structopt = "0.2.4"
-tempdir = "0.3"
 tempfile = "3"
 time = "0.1"
 timebomb = "0.1.2"