Remove more dead code after Object.observe removal

src/contexts.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_CONTEXTS_H_
 #define V8_CONTEXTS_H_
 
 #include "src/heap/heap.h"
 #include "src/objects.h"
 
@@ skipping 93 matching lines @@
   V(JSON_SERIALIZE_ADAPTER_INDEX, JSFunction, json_serialize_adapter)         \
   V(MAKE_ERROR_FUNCTION_INDEX, JSFunction, make_error_function)               \
   V(MAP_DELETE_METHOD_INDEX, JSFunction, map_delete)                          \
   V(MAP_GET_METHOD_INDEX, JSFunction, map_get)                                \
   V(MAP_HAS_METHOD_INDEX, JSFunction, map_has)                                \
   V(MAP_SET_METHOD_INDEX, JSFunction, map_set)                                \
   V(MATH_POW_METHOD_INDEX, JSFunction, math_pow)                              \
   V(MESSAGE_GET_COLUMN_NUMBER_INDEX, JSFunction, message_get_column_number)   \
   V(MESSAGE_GET_LINE_NUMBER_INDEX, JSFunction, message_get_line_number)       \
   V(MESSAGE_GET_SOURCE_LINE_INDEX, JSFunction, message_get_source_line)       \
-  V(NATIVE_OBJECT_GET_NOTIFIER_INDEX, JSFunction, native_object_get_notifier) \
-  V(NATIVE_OBJECT_NOTIFIER_PERFORM_CHANGE, JSFunction,                        \
-    native_object_notifier_perform_change)                                    \
-  V(NATIVE_OBJECT_OBSERVE_INDEX, JSFunction, native_object_observe)           \
   V(NO_SIDE_EFFECTS_TO_STRING_FUN_INDEX, JSFunction,                          \
     no_side_effects_to_string_fun)                                            \
   V(OBJECT_VALUE_OF, JSFunction, object_value_of)                             \
   V(OBJECT_TO_STRING, JSFunction, object_to_string)                           \
   V(PROMISE_CATCH_INDEX, JSFunction, promise_catch)                           \
   V(PROMISE_CHAIN_INDEX, JSFunction, promise_chain)                           \
   V(PROMISE_CREATE_INDEX, JSFunction, promise_create)                         \
   V(PROMISE_FUNCTION_INDEX, JSFunction, promise_function)                     \
   V(PROMISE_HAS_USER_DEFINED_REJECT_HANDLER_INDEX, JSFunction,                \
     promise_has_user_defined_reject_handler)                                  \
@@ skipping 428 matching lines @@
 #endif
 
   STATIC_ASSERT(kHeaderSize == Internals::kContextHeaderSize);
   STATIC_ASSERT(EMBEDDER_DATA_INDEX == Internals::kContextEmbedderDataIndex);
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_CONTEXTS_H_