Apple’s sales remained on a downward slope during the summer, resulting in a full year of declining revenue at the technology trendsetter with a long history of steady growth that turned it into the world’s most valuable publicly traded company. The slight sales deterioration announced Thursday for the July-September period marked the end of Apple’s fiscal year — a stretch that saw the company suffer a revenue decrease from the prior year in each quarter. Although this past fiscal year’s revenue only dipped by 3% from the previous fiscal year, it was still a noteworthy anomaly in a business that…