[ORC] Remove an unused member variable.

Author: lhames

llvm/include/llvm/ExecutionEngine/Orc/MachOPlatform.h

@@ -286,7 +286,6 @@ class LLVM_ABI MachOPlatform : public Platform {
     // FIXME: ObjCImageInfos and HeaderAddrs need to be cleared when
     // JITDylibs are removed.
     DenseMap<JITDylib *, ObjCImageInfo> ObjCImageInfos;
-    DenseMap<JITDylib *, ExecutorAddr> HeaderAddrs;
   };
 
   using GetJITDylibHeaderSendResultFn =