GSB: Remove RequirementSource::usesRequirementSignature
GSB: Remove RequirementSource::usesRequirementSignature

This was only used by the old implementation of getConformanceAccessPath().

Also it wasn't part of the FoldingSet profile, which was potentially a
source of latent bugs.

tkremenek/swift,benlangmuir/swift,glessard/swift,JGiola/swift,parkera/swift,glessard/swift,tkremenek/swift,gregomni/swift,roambotics/swift,atrick/swift,xwu/swift,roambotics/swift,ahoppen/swift,tkremenek/swift,JGiola/swift,xwu/swift,xwu/swift,glessard/swift,roambotics/swift,ahoppen/swift,apple/swift,roambotics/swift,benlangmuir/swift,roambotics/swift,ahoppen/swift,gregomni/swift,atrick/swift,benlangmuir/swift,xwu/swift,rudkx/swift,tkremenek/swift,benlangmuir/swift,rudkx/swift,gregomni/swift,tkremenek/swift,JGiola/swift,ahoppen/swift,atrick/swift,xwu/swift,parkera/swift,apple/swift,hooman/swift,apple/swift,JGiola/swift,glessard/swift,xwu/swift,rudkx/swift,hooman/swift,JGiola/swift,hooman/swift,apple/swift,tkremenek/swift,parkera/swift,rudkx/swift,glessard/swift,ahoppen/swift,gregomni/swift,parkera/swift,tkremenek/swift,parkera/swift,hooman/swift,hooman/swift,atrick/swift,rudkx/swift,rudkx/swift,atrick/swift,gregomni/swift,hooman/swift,benlangmuir/swift,hooman/swift,benlangmuir/swift,JGiola/swift,glessard/swift,parkera/swift,apple/swift,roambotics/swift,parkera/swift,apple/swift,xwu/swift,gregomni/swift,ahoppen/swift,parkera/swift,atrick/swift