Revert "ChildProcessStream: store exitcode/exitsignal"

This reverts commit 7fa9fa5.

Author: blueyed

nvim/session.lua

@@ -181,12 +181,7 @@ function Session:_run(request_cb, notification_cb, timeout)
       self._prepare:stop()
     end)
   end
-  self._msgpack_rpc_stream:read_start(request_cb, notification_cb, function()
-    uv.run()  -- run the loop to get exitcode from child process.
-    self.child_exit = self._msgpack_rpc_stream._stream.exitcode
-    self.child_signal = self._msgpack_rpc_stream._stream.exitsignal
-    uv.stop()
-  end)
+  self._msgpack_rpc_stream:read_start(request_cb, notification_cb, uv.stop)
   uv.run()
   self._prepare:stop()
   self._timer:stop()