Drop no longer used Isolate's default_microtask_queue_address()

As builtins no longer uses default_microtask_queue after
https://crrev.com/c/1369906, Isolate's default_microtask_queue_address()
is no longer needed.

Bug: v8:8124
Change-Id: I1f51e58ada1a62f71f19f6c15b2330dfed176839
Reviewed-on: https://chromium-review.googlesource.com/c/1420178Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Commit-Queue: Taiju Tsuiki <tzik@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58930}

src/external-reference.cc

@@ -137,11 +137,6 @@ ExternalReference ExternalReference::handle_scope_implementer_address(
   return ExternalReference(isolate->handle_scope_implementer_address());
 }
 
-ExternalReference ExternalReference::default_microtask_queue_address(
-    Isolate* isolate) {
-  return ExternalReference(isolate->default_microtask_queue_address());
-}
-
 ExternalReference ExternalReference::interpreter_dispatch_table_address(
     Isolate* isolate) {
   return ExternalReference(isolate->interpreter()->dispatch_table_address());

src/external-reference.h

@@ -27,8 +27,6 @@ class StatsCounter;
   V(builtins_address, "builtins")                                              \
   V(handle_scope_implementer_address,                                          \
     "Isolate::handle_scope_implementer_address")                               \
-  V(default_microtask_queue_address,                                           \
-    "Isolate::default_microtask_queue_address()")                              \
   V(address_of_interpreter_entry_trampoline_instruction_start,                 \
     "Address of the InterpreterEntryTrampoline instruction start")             \
   V(interpreter_dispatch_counters, "Interpreter::dispatch_counters")           \

src/isolate.h

@@ -1433,10 +1433,6 @@ class Isolate final : private HiddenFactory {
     return reinterpret_cast<Address>(&promise_hook_or_async_event_delegate_);
   }
 
-  Address default_microtask_queue_address() {
-    return reinterpret_cast<Address>(&default_microtask_queue_);
-  }
-
   Address promise_hook_or_debug_is_active_or_async_event_delegate_address() {
     return reinterpret_cast<Address>(
         &promise_hook_or_debug_is_active_or_async_event_delegate_);