[snapshot] Remove two unused bytecodes

Bug: 
Change-Id: Ib05bf9abb43872c69102f839876a869c55f8ca48
Reviewed-on: https://chromium-review.googlesource.com/737798Reviewed-by: Peter Marshall <petermarshall@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48915}

src/snapshot/serializer-common.h

@@ -192,9 +192,8 @@ class SerializerDeserializer : public RootVisitor {
   // Used for embedder-allocated backing stores for TypedArrays.
   static const int kOffHeapBackingStore = 0x1c;
 
-  // Used to encode deoptimizer entry code.
-  static const int kDeoptimizerEntryPlain = 0x1d;
-  static const int kDeoptimizerEntryFromCode = 0x1e;
+  // 0x1d, 0x1e unused.
+
   // Used for embedder-provided serialization data for embedder fields.
   static const int kEmbedderFieldsData = 0x1f;