[test] Substring: remove unnecessary `expected` arguments
[test] Substring: remove unnecessary `expected` arguments

The previous commit made these redundant.

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