Removes occurrences of libqt5multimedia because it is properly handled by rosdep

[agalbachicar]

In connection with maliput/delphyne_gui#354

[agalbachicar]

For gcc builds, the following test failed (actually, in the log you'll see two but it is because it evaluates the test itself and the generation of the test report):

• UNIT_agent_simulation_builder_test

I created maliput/delphyne#751 to track the particular case and push it up if it becomes a recurrent problem.