It is much easier for people to help you if you upload the GH file with internalized geometries. (otherwise they have to recreate the whole definition in order to help you.)
pls have a look at this post.
The thinking was to find the faces which had an edge touching the outer perimeter. This could be done by checking the distance between the midpoint of a face edge and the outermost perimeter. If the distance for one of the edge midpoints is 0, then the face is touching.
So first was to join all the faces, get all the naked edges, join them, sort by length and get the longest curve (the outermost perimeter).
Next, taking the naked edges off all the faces and evaluating curve at gives 0.5 gives the mid point.
The Curve Closest Point component gives the distance of these points to the perimeter.
The smallest of all of these values are checked to see if any equal 0 using the Equals component, which gives a True or False output which can then be used to Cull the faces.