backends: remove empty trace-events file

backends: remove empty trace-events file

The content of the backends/trace-events file was entirely
removed in

  commit 6b10e573d15ef82dbc5c5b3726028e6642e134f6
  Author: Marc-André Lureau <marcandre.lureau@redhat.com>
  Date:   Mon May 29 12:39:42 2017 +0400

    char: move char devices to chardev/

Leaving the empty file around, causes tracetool to generate
an empty .dtrace file which makes the dtrace compiler throw
a syntax error.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-id: 20170629162046.4135-1-berrange@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>