Remove support for Object.observe

src/heap-symbols.h

 // Copyright 2015 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_HEAP_SYMBOLS_H_
 #define V8_HEAP_SYMBOLS_H_
 
 #define INTERNALIZED_STRING_LIST(V)                                \
   V(anonymous_string, "anonymous")                                 \
   V(apply_string, "apply")                                         \
@@ skipping 144 matching lines @@
   V(intl_impl_object_symbol)                \
   V(intl_initialized_marker_symbol)         \
   V(intl_pattern_symbol)                    \
   V(intl_resolved_symbol)                   \
   V(megamorphic_symbol)                     \
   V(native_context_index_symbol)            \
   V(nonexistent_symbol)                     \
   V(nonextensible_symbol)                   \
   V(normal_ic_symbol)                       \
   V(not_mapped_symbol)                      \
-  V(observed_symbol)                        \
   V(premonomorphic_symbol)                  \
   V(promise_combined_deferred_symbol)       \
   V(promise_debug_marker_symbol)            \
   V(promise_has_handler_symbol)             \
   V(promise_on_resolve_symbol)              \
   V(promise_on_reject_symbol)               \
   V(promise_raw_symbol)                     \
   V(promise_status_symbol)                  \
   V(promise_value_symbol)                   \
   V(sealed_symbol)                          \
@@ skipping 16 matching lines @@
 // Well-Known Symbols are "Public" symbols, which have a bit set which causes
 // them to produce an undefined value when a load results in a failed access
 // check. Because this behaviour is not specified properly as of yet, it only
 // applies to a subset of spec-defined Well-Known Symbols.
 #define WELL_KNOWN_SYMBOL_LIST(V)                           \
   V(has_instance_symbol, Symbol.hasInstance)                \
   V(is_concat_spreadable_symbol, Symbol.isConcatSpreadable) \
   V(to_string_tag_symbol, Symbol.toStringTag)
 
 #endif  // V8_HEAP_SYMBOLS_H_