Revert of [heap] Unify the immortal immovable root detection mechanism.

src/unique.h

Index: src/unique.h
diff --git a/src/unique.h b/src/unique.h
index 649eb343dad0795bdaa3227327fe3ec8b746afa8..61d57d01ff53388a22efad6bbb2575c8870fe30e 100644
--- a/src/unique.h
+++ b/src/unique.h
@@ -129,11 +129,6 @@
     return Unique<T>(reinterpret_cast<Address>(*handle), handle);
   }
 
-  T* GetRawAddress() const {
-    DCHECK(IsInitialized());
-    return reinterpret_cast<T*>(raw_address_);
-  }
-
   friend class UniqueSet<T>;  // Uses internal details for speed.
   template <class U>
   friend class Unique;  // For comparing raw_address values.