how do i undo the rig?

1st armature, rig, skeleton and bones = the same thing

2nd Pose and animation = almost the same thing... if you think of the old type flip books then animation is just a set of X poses running one after the other

assumes Blender but most 3d software has the same options

• best and most basic way to remove animation is to untick the select box when you import the model [see above image]
• the worse possible way is to select either the pose or animation layer and just hit delete because all kinds of junk gets left behind and the scale also tends to go haywire [see images below]