greybus: connection: remove unused time-stamp defines

Remove unused time-stamp defines, that were left in when the time-stamp
fifo was removed.

Signed-off-by: Johan Hovold <johan@hovoldconsulting.com>
Reviewed-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>