[IRGen] Remove unused ExistentialTypeInfoBase::findWitnessTable
[IRGen] Remove unused ExistentialTypeInfoBase::findWitnessTable

Turns out we never ask this of TypeInfo anymore.

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