7 RHA was officialy re-titled 7th Parachute Regiment Royal Horse Artillery in 1987*, so the "Parachute" part is indeed part of the title, and "7 Para RHA" is the correct abbreviation.
"7 RHA" (and sometimes "7 Para") happens to roll off the tongue better, and so is in common use.
(the then- adjutant John Murphy had the honour of being first to use the title when calling the "re-naming parade" to attention after the CO had made the announcement. If anyone is old enough to remember that day... )