Revert^5 "Rewrite JVMTI method tracing to use trampolines"

This reverts commit d7da3147fea647ade418337aed6a8f9402412611.

Reason for revert: Tests are still failing on the buildbot.

Change-Id: Iaaac38137b1c4bed8e3a15b0c0c14730654025f6
diff --git a/runtime/jit/jit.cc b/runtime/jit/jit.cc
index 86f0606..ed449b5 100644
--- a/runtime/jit/jit.cc
+++ b/runtime/jit/jit.cc
@@ -768,20 +768,13 @@
 void Jit::Stop() {
   Thread* self = Thread::Current();
   // TODO(ngeoffray): change API to not require calling WaitForCompilationToFinish twice.
-  // During shutdown and startup the thread-pool can be null.
-  if (GetThreadPool() == nullptr) {
-    return;
-  }
   WaitForCompilationToFinish(self);
   GetThreadPool()->StopWorkers(self);
   WaitForCompilationToFinish(self);
 }
 
 void Jit::Start() {
-  // During shutdown and startup the thread-pool can be null.
-  if (GetThreadPool() != nullptr) {
-    GetThreadPool()->StartWorkers(Thread::Current());
-  }
+  GetThreadPool()->StartWorkers(Thread::Current());
 }
 
 ScopedJitSuspend::ScopedJitSuspend() {