A part from the use of Goliath demolition tanks, I don't know of any provision for eliminating entrenchments. I suspect it is a misprint. Change the word "eliminated" to "controlled", and the victory conditions will make more sense.
... More and more, people around the world are coming to realize that the world is flat!
I think the point is that the word "elimination," as far as an entrenchment is concerned regarding the OP's question, is to be interpreted in game play as change of (or loss of ) possession rather than "removed from play."