edition: Remove extern crate lines

In Rust 2018 edition, `extern crate` is no longer required for importing
from other crates. Instead of writing:

    extern crate dep;
    use dep::Thing;

we write:

    use dep::Thing;

In this approach, macros are imported individually from the declaring
crate rather than through #[macro_use]. Before:

    #[macro_use]
    extern crate sys_util;

After:

    use sys_util::{debug, error};

The only place that `extern crate` continues to be required is in
importing the compiler's proc_macro API into a procedural macro crate.
This will hopefully be fixed in a future Rust release.

    extern crate proc_macro;

TEST=cargo check
TEST=cargo check --all-features
TEST=cargo check --target aarch64-unknown-linux-gnu
TEST=local kokoro

Change-Id: I0b43768c0d81f2a250b1959fb97ba35cbac56293
Reviewed-on: https://chromium-review.googlesource.com/1565302
Commit-Ready: David Tolnay <dtolnay@chromium.org>
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Tested-by: David Tolnay <dtolnay@chromium.org>
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: David Tolnay <dtolnay@chromium.org>

3 files changed, 1 insertions, 14 deletions

diff --git a/msg_socket/tests/enum.rs b/msg_socket/tests/enum.rs
index 9134f6e..b4c7189 100644
--- a/msg_socket/tests/enum.rs
+++ b/msg_socket/tests/enum.rs
@@ -1,7 +1,3 @@
-extern crate msg_on_socket_derive;
-extern crate msg_socket;
-extern crate sys_util;
-
 use sys_util::EventFd;
 
 use msg_socket::*;
diff --git a/msg_socket/tests/struct.rs b/msg_socket/tests/struct.rs
index a2d5c9c..2cc9d37 100644
--- a/msg_socket/tests/struct.rs
+++ b/msg_socket/tests/struct.rs
@@ -1,7 +1,3 @@
-extern crate msg_on_socket_derive;
-extern crate msg_socket;
-extern crate sys_util;
-
 use sys_util::EventFd;
 
 use msg_socket::*;
diff --git a/msg_socket/tests/tuple.rs b/msg_socket/tests/tuple.rs
index 717cd91..b388328 100644
--- a/msg_socket/tests/tuple.rs
+++ b/msg_socket/tests/tuple.rs
@@ -1,10 +1,5 @@
-extern crate msg_on_socket_derive;
-extern crate msg_socket;
-extern crate sys_util;
-
-use sys_util::EventFd;
-
 use msg_socket::*;
+use sys_util::EventFd;
 
 #[derive(MsgOnSocket)]
 struct Message(u8, u16, EventFd);