Calm down, children!
BA could, and did, legally de-activate the No. 3 door emergency exits on their 747-200s because their maximum passenger capacity allowed them to do so. While I don't know what the seating capacity on those aircraft was, it was considerably less than that of some of their competitors, who could therefore not reduce the exits. As an example, some of Virgin's high-density-fit Classics (used for Orlando and Caribbean flights) were capable of carrying 500 or so passengers; no way could they have lost those exits.
As I remember, BA's decision to reduce the number of exits did cause some controversy at the time, but, as others have shown, it was declared legal and acceptable by the CAA at the time. There were, of course, both weight and staffing advantages.
Most operators retained the 10 lower-deck exits. I'm only aware of BA having de-activated any, though I may be wrong. There are, of course, many Classic 747s still in service around the world, but BA's last 9 were withdrawn between September 2001 and Jan 2002, as far as I can remember.