[stdlib] Substring: remove _encodedOffsetRange in favor of existing _offsetRange
[stdlib] Substring: remove _encodedOffsetRange in favor of existing _offsetRange

ahoppen/swift,gregomni/swift,benlangmuir/swift,apple/swift,atrick/swift,roambotics/swift,glessard/swift,glessard/swift,apple/swift,JGiola/swift,glessard/swift,roambotics/swift,ahoppen/swift,ahoppen/swift,benlangmuir/swift,atrick/swift,atrick/swift,ahoppen/swift,roambotics/swift,gregomni/swift,benlangmuir/swift,roambotics/swift,roambotics/swift,apple/swift,benlangmuir/swift,atrick/swift,atrick/swift,ahoppen/swift,ahoppen/swift,gregomni/swift,glessard/swift,benlangmuir/swift,gregomni/swift,apple/swift,JGiola/swift,roambotics/swift,benlangmuir/swift,glessard/swift,JGiola/swift,JGiola/swift,apple/swift,JGiola/swift,apple/swift,gregomni/swift,atrick/swift,glessard/swift,gregomni/swift,JGiola/swift