At least Lou Grant was the kind of grumpy boss a gal could love. In playwright Neil Simon, MARY TYLER MOORE seems to have a harsher critic. After receiving a note from Simon last week slamming her performance in his new comedy, Rose's Dilemma, Moore withdrew from the off-Broadway play, scheduled to open Dec. 18. "Mary was devastated and completely debilitated personally and professionally," says her publicist's statement. If she had just pouted and whined "Oh, Mr. Simon," none of this might have transpired.