Make an internal KeyPath helper final.
Make an internal KeyPath helper final.

And remove an unnecessary override, so that further work will allow this method not to need a
vtable entry.

tkremenek/swift,CodaFi/swift,jckarter/swift,hooman/swift,gregomni/swift,rudkx/swift,stephentyrone/swift,apple/swift,nathawes/swift,JGiola/swift,ahoppen/swift,jmgc/swift,rudkx/swift,apple/swift,ahoppen/swift,JGiola/swift,parkera/swift,CodaFi/swift,CodaFi/swift,xwu/swift,jckarter/swift,atrick/swift,xwu/swift,gregomni/swift,hooman/swift,benlangmuir/swift,parkera/swift,parkera/swift,apple/swift,airspeedswift/swift,hooman/swift,tkremenek/swift,nathawes/swift,tkremenek/swift,atrick/swift,JGiola/swift,allevato/swift,rudkx/swift,airspeedswift/swift,benlangmuir/swift,CodaFi/swift,benlangmuir/swift,parkera/swift,stephentyrone/swift,atrick/swift,allevato/swift,glessard/swift,jckarter/swift,apple/swift,tkremenek/swift,JGiola/swift,roambotics/swift,airspeedswift/swift,gregomni/swift,jmgc/swift,roambotics/swift,allevato/swift,nathawes/swift,jckarter/swift,jmgc/swift,benlangmuir/swift,CodaFi/swift,hooman/swift,jckarter/swift,xwu/swift,jckarter/swift,roambotics/swift,atrick/swift,hooman/swift,airspeedswift/swift,parkera/swift,rudkx/swift,nathawes/swift,jmgc/swift,parkera/swift,rudkx/swift,parkera/swift,gregomni/swift,rudkx/swift,jmgc/swift,allevato/swift,JGiola/swift,benlangmuir/swift,tkremenek/swift,stephentyrone/swift,xwu/swift,xwu/swift,apple/swift,CodaFi/swift,atrick/swift,hooman/swift,gregomni/swift,gregomni/swift,allevato/swift,nathawes/swift,jmgc/swift,airspeedswift/swift,CodaFi/swift,stephentyrone/swift,jmgc/swift,xwu/swift,nathawes/swift,airspeedswift/swift,glessard/swift,ahoppen/swift,jckarter/swift,tkremenek/swift,glessard/swift,roambotics/swift,apple/swift,ahoppen/swift,nathawes/swift,atrick/swift,allevato/swift,stephentyrone/swift,allevato/swift,parkera/swift,stephentyrone/swift,roambotics/swift,ahoppen/swift,stephentyrone/swift,ahoppen/swift,JGiola/swift,hooman/swift,glessard/swift,benlangmuir/swift,xwu/swift,roambotics/swift,glessard/swift,glessard/swift,airspeedswift/swift,tkremenek/swift