Update LLVM development policy
Update LLVM development policy

State explicitly that we want to eliminate all differences between
`apple/master` and `llvm.org/master`. All new LLVM development should happen
upstream.

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