[AST] Minor cleanups to SubstitutionMap.
[AST] Minor cleanups to SubstitutionMap.

huonw/swift,roambotics/swift,lorentey/swift,karwa/swift,harlanhaskins/swift,alblue/swift,CodaFi/swift,devincoughlin/swift,natecook1000/swift,CodaFi/swift,karwa/swift,hooman/swift,roambotics/swift,shajrawi/swift,lorentey/swift,atrick/swift,danielmartin/swift,benlangmuir/swift,JGiola/swift,apple/swift,jmgc/swift,alblue/swift,danielmartin/swift,sschiau/swift,brentdax/swift,rudkx/swift,danielmartin/swift,sschiau/swift,stephentyrone/swift,huonw/swift,devincoughlin/swift,devincoughlin/swift,austinzheng/swift,xedin/swift,shahmishal/swift,roambotics/swift,practicalswift/swift,jopamer/swift,roambotics/swift,ahoppen/swift,aschwaighofer/swift,hooman/swift,nathawes/swift,xwu/swift,sschiau/swift,CodaFi/swift,glessard/swift,natecook1000/swift,nathawes/swift,hooman/swift,karwa/swift,jopamer/swift,ahoppen/swift,shajrawi/swift,gribozavr/swift,lorentey/swift,shajrawi/swift,sschiau/swift,benlangmuir/swift,stephentyrone/swift,natecook1000/swift,alblue/swift,allevato/swift,CodaFi/swift,tkremenek/swift,harlanhaskins/swift,rudkx/swift,JGiola/swift,shahmishal/swift,alblue/swift,parkera/swift,gribozavr/swift,danielmartin/swift,parkera/swift,harlanhaskins/swift,apple/swift,jckarter/swift,JGiola/swift,practicalswift/swift,brentdax/swift,karwa/swift,huonw/swift,rudkx/swift,gribozavr/swift,xedin/swift,xwu/swift,xedin/swift,parkera/swift,hooman/swift,glessard/swift,gregomni/swift,aschwaighofer/swift,xedin/swift,amraboelela/swift,alblue/swift,nathawes/swift,airspeedswift/swift,hooman/swift,allevato/swift,shahmishal/swift,devincoughlin/swift,huonw/swift,harlanhaskins/swift,benlangmuir/swift,devincoughlin/swift,stephentyrone/swift,nathawes/swift,shajrawi/swift,xedin/swift,allevato/swift,parkera/swift,atrick/swift,nathawes/swift,ahoppen/swift,harlanhaskins/swift,CodaFi/swift,atrick/swift,lorentey/swift,lorentey/swift,atrick/swift,tkremenek/swift,amraboelela/swift,rudkx/swift,gregomni/swift,practicalswift/swift,karwa/swift,shahmishal/swift,danielmartin/swift,danielmartin/swift,jckarter/swift,airspeedswift/swift,glessard/swift,aschwaighofer/swift,rudkx/swift,practicalswift/swift,natecook1000/swift,sschiau/swift,jckarter/swift,hooman/swift,gregomni/swift,xedin/swift,jmgc/swift,hooman/swift,benlangmuir/swift,airspeedswift/swift,alblue/swift,devincoughlin/swift,stephentyrone/swift,jopamer/swift,jmgc/swift,gribozavr/swift,practicalswift/swift,shajrawi/swift,jmgc/swift,gregomni/swift,jopamer/swift,CodaFi/swift,lorentey/swift,stephentyrone/swift,glessard/swift,sschiau/swift,parkera/swift,atrick/swift,huonw/swift,apple/swift,gregomni/swift,nathawes/swift,jckarter/swift,harlanhaskins/swift,parkera/swift,gribozavr/swift,xedin/swift,jckarter/swift,practicalswift/swift,harlanhaskins/swift,shahmishal/swift,amraboelela/swift,allevato/swift,xwu/swift,sschiau/swift,devincoughlin/swift,shahmishal/swift,jopamer/swift,parkera/swift,ahoppen/swift,ahoppen/swift,allevato/swift,amraboelela/swift,karwa/swift,gribozavr/swift,austinzheng/swift,jmgc/swift,aschwaighofer/swift,apple/swift,xwu/swift,brentdax/swift,lorentey/swift,natecook1000/swift,brentdax/swift,parkera/swift,austinzheng/swift,allevato/swift,JGiola/swift,alblue/swift,jopamer/swift,nathawes/swift,xwu/swift,xwu/swift,aschwaighofer/swift,lorentey/swift,devincoughlin/swift,amraboelela/swift,airspeedswift/swift,benlangmuir/swift,rudkx/swift,apple/swift,airspeedswift/swift,tkremenek/swift,glessard/swift,brentdax/swift,benlangmuir/swift,airspeedswift/swift,stephentyrone/swift,austinzheng/swift,shajrawi/swift,tkremenek/swift,gribozavr/swift,aschwaighofer/swift,tkremenek/swift,shajrawi/swift,apple/swift,shahmishal/swift,gribozavr/swift,xedin/swift,jopamer/swift,shajrawi/swift,huonw/swift,glessard/swift,danielmartin/swift,allevato/swift,ahoppen/swift,natecook1000/swift,huonw/swift,xwu/swift,roambotics/swift,jmgc/swift,amraboelela/swift,shahmishal/swift,atrick/swift,austinzheng/swift,stephentyrone/swift,practicalswift/swift,sschiau/swift,CodaFi/swift,JGiola/swift,jmgc/swift,austinzheng/swift,practicalswift/swift,karwa/swift,jckarter/swift,aschwaighofer/swift,JGiola/swift,amraboelela/swift,roambotics/swift,tkremenek/swift,jckarter/swift,brentdax/swift,austinzheng/swift,gregomni/swift,brentdax/swift,natecook1000/swift,karwa/swift,tkremenek/swift,airspeedswift/swift