Based on the description and pictures, I would guess that they are part of some sort of hinge. Especially if the silver bar inside rotates 90° along the plane of installation (i.e. in the direction necessary for it to act as a pivot point of a hinge).
The 2nd picture, if it has a matching one at the top of the opening shown, would make sense as the pivot points of a door that covers the opening.
The 1st picture, if it also has a matching one at the other side of the opening shown, would make sense as the pivot point of a lift-up door covering the opening. A lift up door would be rather inconvenient, so maybe the part that attaches to the door itself also has a slide mechanism, so the door can be lifted then pushed back into the cabinet, above the opening shown, so it's out of the way.
I would say that if you don't have the matching door hardware, these will be of little use to you and could, therefore, be removed. However, I'd continue searching to see if you can identify them, and if so, if you can find a source for the "door part" of the hinge mechanism. I don't know how old this particular cabinet it, but restoring it to its original hardware configuration would surely improve its value, and, at a minimum, would help create a conversation piece.
On the other hand, if you do remove them, you'll probably want to patch the holes left behind, and that's a lot of unnecessary work to cover up something that could easily be left in place without impacting future use of the cabinet. Even if you can't identify this hardware now, you never know when you may have a guest over who takes one look at it and says, "I haven't seen a ___ like that in ages!!", then you'll know exactly what it is!
You may also have better luck asking on Woodworking, as there are quite a few there who are pretty darn knowledgeable about old tools, cabinet making, etc. and may have seen something like this.