I had the issue with "2 Olde Mill Lane".
I've tried it on a few other lots (both empty and build on) and the stairs were removeable. Then I tried to go back to the main menu and got stuck on the loading screen again.
After manually shutting the game down and reloading, I tried it in my current game in "2 Olde Mill Lane" and couldn't remove the stairs again & got stuck on the loading screen.
After another reload I tried it again and at first I could remove the stairs in my active lot. Then I travelled to another lot (Bargain Bend) and tried it. I could remove the stairs. I went back to "2 Olde Mill Lane" where I once again couldn't remove the stairs and got stuck on the next loading screen.