Remove the signalfd backend

This backend appears to miss some signals that are raised on other
threads. This might be the cause of smol-rs/async-process#55.

I don't feel like kneading signalfd into a better shape, and it probably
isn't much of an improvement over the pipe strategy anyways. So I've just
removed it.

Signed-off-by: John Nunley <dev@notgull.net>

Cargo.toml

@@ -34,9 +34,6 @@ features = [
     "Win32_System_Console",
 ]
 
-[target.'cfg(any(target_os = "android", target_os = "linux"))'.dependencies]
-concurrent-queue = "2.2.0"
-
 [dev-dependencies]
 async-io = "1.12.0"
 fastrand = "2.0.1"

src/lib.rs

@@ -57,13 +57,7 @@
 )]
 
 cfg_if::cfg_if! {
-    if #[cfg(async_signal_force_pipe_impl)] {
-        mod pipe;
-        use pipe as sys;
-    } else if #[cfg(any(target_os = "android", target_os = "linux"))] {
-        mod signalfd;
-        use signalfd as sys;
-    } else if #[cfg(windows)] {
+    if #[cfg(windows)] {
         mod channel;
         use channel as sys;
     } else {