[Clang importer] Remove the OS_object objc_runtime_visible hack.
[Clang importer] Remove the OS_object objc_runtime_visible hack.

The Clang importer has an old hack that makes OS_object and its subclasses
implicitly "objc_runtime_visible" (which maps to the "runtime" foreign
class kind in Swift). Now that the headers in the SDK all use the
appropriate annotation, remove the hack.

Fixes rdar://problem/64778416.

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