Revert "This implements per-isolate locking and unlocking, including tests"

src/execution.cc

Index: src/execution.cc
diff --git a/src/execution.cc b/src/execution.cc
index d511b9015882fea11911ef874ce308906ad42415..eb26438fe87af6a1d264b3b9ad32ad0efab6e8e8 100644
--- a/src/execution.cc
+++ b/src/execution.cc
@@ -457,9 +457,8 @@ void StackGuard::ClearThread(const ExecutionAccess& lock) {
 
 void StackGuard::InitThread(const ExecutionAccess& lock) {
   if (thread_local_.Initialize()) isolate_->heap()->SetStackLimits();
-  Isolate::PerIsolateThreadData* per_thread =
-      isolate_->FindOrAllocatePerThreadDataForThisThread();
-  uintptr_t stored_limit = per_thread->stack_limit();
+  uintptr_t stored_limit =
+      Isolate::CurrentPerIsolateThreadData()->stack_limit();
   // You should hold the ExecutionAccess lock when you call this.
   if (stored_limit != 0) {
     StackGuard::SetStackLimit(stored_limit);