Remove promotion backup case and report OOM instead.

src/heap/heap.cc

Index: src/heap/heap.cc
diff --git a/src/heap/heap.cc b/src/heap/heap.cc
index 26cffc8fb5524e51310776f74c2fbc3e0e7edf8b..aab5cab772edf2032bbba7420b300617cbc534b0 100644
--- a/src/heap/heap.cc
+++ b/src/heap/heap.cc
@@ -2200,11 +2200,7 @@ class ScavengingVisitor : public StaticVisitorBase {
                                                   object_size)) {
       return;
     }
-
-    // If promotion failed, we try to copy the object to the other semi-space
-    if (SemiSpaceCopyObject<alignment>(map, slot, object, object_size)) return;
-
-    UNREACHABLE();
+    V8::FatalProcessOutOfMemory("Scavenge promotion failed");
   }