Get rid of UnsafeCurrent in Sampler

src/isolate.h

Index: src/isolate.h
diff --git a/src/isolate.h b/src/isolate.h
index 015f861301b1b05e48b8efbc5955a236147a17fe..74122db7cc333826363f78269ee76d4dad42b267 100644
--- a/src/isolate.h
+++ b/src/isolate.h
@@ -495,14 +495,6 @@ class Isolate {
     return isolate;
   }
 
-  // Like Current, but skips the check that |isolate_key_| was initialized.
-  // Callers have to ensure that themselves.
-  // DO NOT USE. The only remaining callsite will be deleted soon.
-  INLINE(static Isolate* UnsafeCurrent()) {
-    return reinterpret_cast<Isolate*>(
-        base::Thread::GetThreadLocal(isolate_key_));
-  }
-
   // Usually called by Init(), but can be called early e.g. to allow
   // testing components that require logging but not the whole
   // isolate.