Jonathan,
The original post on this subject was titled catapult extensions which some folks called horns, booms, and most recently in your post, arresting gear harnesses. They are in fact bridle arrestor booms. The Kitty Hawk and other four catapult carriers never had four, only three for Cats 1,2 & 3. The 'booms' were used to house energy absorbers early on (MK-1) and later bridle arrester track topside (Mk-2 & 4). The bridle arrester systems were not used for nose gear launch equipped aircraft which began with the A-7 up to and including the Hornet Series.
The A-7 being obsolete had nothing to do with the 'booms' being removed. They were removed for two primary reasons:
1) Bridle/pendant type aircraft were no longer in air wing inventory.
2) Topside weight removal. Beginning in the mid-80s there was a concerted effort in the carrier Navy to get rid of any and all unneccessary topside weight. Getting rid of the booms, machinery and topside track was a considerable step in the right direction.
Retaining a boom or two for a "just in case" scenario has some validity however the reason has nothing to do with Hornets. When the training carrier (the Lexington) was approaching decomissioning, it was expected that east coast CVs (primarily JFK) would rotate the duty however there was a possibility the Training Command would come to the west coast (and they did at least once). At the time the training command was still using T-29s (?) and A-4s, both bridle launch aircraft so it was prudent that several west coast carriers retain at least one boom and bridle arrester capability on Cat 1. After much start up problems, the Training Command finally transitioned to the T45 which is a nose gear launch aircraft and the need for the booms/bridle arresters disappeared.