It's in a right click menu. You have to select it.
One is specifically right clicking the menu in order to delete files from Playing Now by selecting Remove.
You can see below that the Remove From List and Clear Playing Now commands are right next to each other and it is easy to click the wrong command. Also, using the Delete key instead of clicking Remove doesn't work well when one is using a mouse.
Before the change, you had to right click the Playing Now
zone to select Clear Playing Now and now you can clear your files directly from the
list itself.
I edit my Playing Now in Theater View but can see how this could be a problem with Standard View.