How to remove this galvenized pipe?
Considering the age of the pipe and the odds of it being so rusted inside as to be nearly useless, I would consider now a good time to improve the drain! I would first look at what I had to cut the pipe, rather than try to fight it loose! One easy step is to grind it off if no other metal cutting tools are available. Then I would start building back with materials meant for drains. Cast iron was once common but newer builds will be plastic of various types which do not rust and clog so easily.
This drain is a real bear to deal with.
When you have a bear trapped in the cabin, it is often best to just shoot it!