Sorry to say but you cannot shorten a link because it is generated by Bing. The pictures and adds that you see on the lock screen are downloaded by Windows Spotlight from Bing to display on your lock screen.
However, you can hide these advertisements.
Go to Settings - Personalization - Lock screen
Select either Picture or Slideshow under Background
Scroll down to Get fun facts, tips, tricks, and more on your lock screen and set Off position.
Select Spotlight under background.
Reboot the computer and check if adds are removed.