paho-mqtt-c: bump to version 1.3.0

paho-mqtt-c: bump to version 1.3.0

paho-mqtt-c 1.3.0 is the current stable version of paho-mqtt-c.

The patch 0001-Declare-mqtt-tests-as-a-C-only-project.patch is no longer
required, a similar fix was applied upstream with:
a87450ebcefed573ad4cdac77e2c893a3c314762.

Signed-off-by: Julien Grossholtz <julien.grossholtz@openest.io>
Reviewed-by: Yegor Yefremov <yegorslists@googlemail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>