The requirement to use ther word "heavy" has been around since the late 70s, but ignored by most.
It's still in CAP 413 (Chapter 2, Page 8, 1.8.5) "Aircraft in the heavy wake vortex category shall include the word "HEAVY" immediately after the aircraft callsign in the initial call to each ATSU."
Times have moved on though and I agree with Bol Zup that it is unnecessary now that the wake category is displayed on the FPS.
letMfly