[Frontend] NFC: Remove an outdated comment
[Frontend] NFC: Remove an outdated comment

`performParseOnly` has been able to handle
multiple input files for a while now.

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