I have removed a stair wall but not sure if it was a load bearing wall or not.
This may sound like a trivial answer, but - you should just check.
With the authorities
In many (most?) states in the world, house construction plans must be submitted to a local/regional planning body where they are kept in an archive. go get a copy. The plans should somehow (fingers crossed) indicate which walls bear load.
It's probably a good idea to have a copy of those plans anyway.
Consult a professional
Find a home constructor - or a company which does home construction - and ask them to determine that for you. They will probably take a bit of money, but not that much.
Show them the plans if you have them!
Newbie sentiment: Better to feel sorry for wasting a bit of money than to feel sorry for cracks or a collapse of part of your house.