auto merge of #17673 : aturon/rust/remove-uv, r=alexcrichton

This PR begins the process of [runtime removal](rust-lang/rfcs#230) by dismantling the `librustuv` crate and associated event loop.

The result is that, while `libgreen` can still be used for task scheduling purposes, it will no longer be feasible to use green-threaded I/O.

Removing the libuv-based event loop eases the transition away from the runtime system, which will be done incrementally.

In terms of visible API changes, this PR:

* Removes `std::io::signal`, which was never implemented on the native threading model.

* Removes the `iotest!` macro, which was previously used to run I/O tests on both green and native threading models.

* Removes the `green_start!` macro for starting an application with a `librustuv` event loop.

* Removes the `librustuv` crate itself.

It also removes the `libuv` and `gyp` submodules and adjusts the build system and copyright notices accordingly.

If you wish to continue using `librustuv` and green-threaded I/O, consider using [green-rs](https://github.com/alexcrichton/green-rs/), which provides its own I/O stack.

Author: bors

.gitmodules

@@ -2,13 +2,6 @@
 	path = src/llvm
 	url = https://github.com/rust-lang/llvm.git
 	branch = master
-[submodule "src/libuv"]
-	path = src/libuv
-	url = https://github.com/rust-lang/libuv.git
-	branch = master
-[submodule "src/gyp"]
-	path = src/gyp
-	url = https://github.com/rust-lang/gyp.git
 [submodule "src/compiler-rt"]
 	path = src/compiler-rt
 	url = https://github.com/rust-lang/compiler-rt.git

COPYRIGHT

@@ -213,41 +213,6 @@ their own copyright notices and license terms:
   as the Rust compiler or runtime libraries themselves).
 
 
-* The libuv asynchronous I/O library. Code for this package
-  is found in the src/libuv directory, within this
-  distribution. This package is redistributed under the
-  following terms, as noted in its source:
-
-    Copyright Joyent, Inc. and other Node contributors. All
-    rights reserved.  Permission is hereby granted, free of
-    charge, to any person obtaining a copy of this software
-    and associated documentation files (the "Software"), to
-    deal in the Software without restriction, including
-    without limitation the rights to use, copy, modify,
-    merge, publish, distribute, sublicense, and/or sell
-    copies of the Software, and to permit persons to whom
-    the Software is furnished to do so, subject to the
-    following conditions:
-
-    The above copyright notice and this permission notice
-    shall be included in all copies or substantial portions
-    of the Software.
-
-    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF
-    ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED
-    TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
-    PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT
-    SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
-    CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
-    OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR
-    IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
-    DEALINGS IN THE SOFTWARE.
-
-
-* Additional libraries included in libuv carry separate
-  BSD-compatible licenses. See src/libuv/LICENSE for
-  details.
-
 * The src/rt/miniz.c file, carrying an implementation of
   RFC1950/RFC1951 DEFLATE, by Rich Geldreich
   <richgel99@gmail.com>. All uses of this file are