Remove unwanted support of GTestDbus

As newport is on demand service, No need to start it
explicitly using GTestDbus.

Apertis: https://phabricator.apertis.org/T3833



Reviewed-by: Simon McVittie <simon.mcvittie@collabora.co.uk>
Signed-off-by: Rohan Madgula <Rohan.Madgula@in.bosch.com>
Differential Revision: https://phabricator.apertis.org/D6472