No, don't eliminate the relay. The horn draws about 20A when you're honking it. I'm assuming that since you went to the trouble of installing an add-on fuse box that you plan on having other electrical stuff going on. The PC-8 can handle 20A max on any one circuit, with 60A max (40A switched 20A un-switced). If you were, for example, running at night with driving lights and heated gear, it is not inconceivable that you could max out the panel when adding the horn. Even if you don't, the horn is one accessory I just always leave out off the fuse panel. On top of all of that, the relay in the fuse panel will be 'on' the entire time the bike is switched on. The point of the relay on the horn is to have it not be energized until you actually pushy the horn button.
Wire the horn separately with direct-to-battery power and a 30A relay on the OEM horn circuit.