Should I let my professor know that I cited a text written by him....that I pirated from online I wrote an essay for a professor of mine, in which I cited a book he had written. As it so happens, the citation is based on my having obtained a (most likely) pirated PDF copy of the book. The text is quite expensive, not readily available anywhere (library, textbook store, or Amazon) aside from the publisher, and the subject matter is esoteric and poorly addressed in other papers. I am only citing less than 10 pages worth of material, mostly on definitions and problem formulation

I am going to be presenting this essay in front of the class, and my concern is that he will notice the citation of his book and ask the potentially uncomfortable question of "...so you have one of my books...?"

I'm wondering what I should do in this case. Should I simply remove all references to the problem texts and cited portions and pretend that nothing ever happened? Should I not do anything? Is the citation of a text that you pirated really a big deal in academia?
It is incredibly uncommon to assume that someone bought a book just because it is cited. While in theory, the professor could ask this question, why would (s)he care? 
If you are geniuinely concerned about the question, perform an inter-library loan with your university library on the two books now, and should that question ideed pop up, reply that you performed an inter-library loan.
Use legal sources in the future. Libraries spend tons of money on buying literature, so use it. Most jurisdictions also allow limited copying of a book (e.g., the most relevant pages for your own work).