greybus: core: remove uevent handling for gb_connection

As we are going to be removing the struct device from gb_connection,
there is no need to do anything for uevents for them.  So just remove
the code.  It wasn't doing anything anyway, so no functionality is lost
here at all.

As is_gb_connection() is no longer used, that is also removed in this
patch.

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