[CodeGen] Remove an outdated comment in MachinePointerInfo

This comment has been untrue since D39758 changed
MachinePointerInfo to store AddrSpace separately from V.

Author: jayfoad

llvm/include/llvm/CodeGen/MachineMemOperand.h

@@ -37,8 +37,6 @@ class ModuleSlotTracker;
 /// as frame indices) that are exposed during codegen.
 struct MachinePointerInfo {
   /// This is the IR pointer value for the access, or it is null if unknown.
-  /// If this is null, then the access is to a pointer in the default address
-  /// space.
   PointerUnion<const Value *, const PseudoSourceValue *> V;
 
   /// Offset - This is an offset from the base Value*.