Remove compile_error in pipe module

Initially I though this would give a nice error message saying that
platform X wasn't supported. But due to the amount of other errors the
error message is still not great.

So, to make porting easier in the future, just remove this and we'll get
a `fds` not defined error.

src/sys/unix/pipe.rs

@@ -58,30 +58,6 @@ pub(crate) fn new_raw() -> io::Result<[RawFd; 2]> {
         }
     }
 
-    #[cfg(not(any(
-        target_os = "aix",
-        target_os = "android",
-        target_os = "dragonfly",
-        target_os = "freebsd",
-        target_os = "fuchsia",
-        target_os = "haiku",
-        target_os = "illumos",
-        target_os = "ios",
-        target_os = "linux",
-        target_os = "macos",
-        target_os = "netbsd",
-        target_os = "openbsd",
-        target_os = "redox",
-        target_os = "tvos",
-        target_os = "visionos",
-        target_os = "watchos",
-        target_os = "espidf",
-        target_os = "solaris",
-        target_os = "vita",
-        target_os = "nto",
-    )))]
-    compile_error!("unsupported target for `mio::unix::pipe`");
-
     Ok(fds)
 }