how to recall a request for recommendation letter from professor
Why not just write what you just did?


  Dear Professor X,
  A while ago we talked about whether you would be willing to write a letter of recommendation for me. I have given this some more thought and have decided, instead of going to graduate school, to try to find a job in industry instead in order to get more work experience. For the time being, at least, I will therefore not need your letter after all, though I appreciate your willingness to provide one. I might come back to your offer at a later time if I decide to go back to graduate school!
  Sincerely, Y