Remove prints in get_overall_test_result()

If we need to know the individual tests results of each CPU then it
would be better to store them in the test report in non-volatile memory.
At the moment, we only store the overall test result, which seems to
provide enough information.

Change-Id: I7429a07062705244eca9c7587bd7c92c468464eb
Signed-off-by: Sandrine Bailleux <sandrine.bailleux@arm.com>