Reapply "A simpler scheme for garbage collection of ureachable phi inputs."

runtime/vm/growable_array.h

Index: runtime/vm/growable_array.h
diff --git a/runtime/vm/growable_array.h b/runtime/vm/growable_array.h
index 7a2b7b266226f3742d820e78f63a69c1d238335b..965651e2a33e91a24a30dee0f4e7add816e1dda9 100644
--- a/runtime/vm/growable_array.h
+++ b/runtime/vm/growable_array.h
@@ -73,14 +73,6 @@ class BaseGrowableArray : public B {
     length_ = 0;
   }
 
-  void RemoveFirst() {
-    ASSERT(length_ > 0);
-    length_--;
-    for (int i = 0; i < length_; i++) {
-      data_[i] = data_[i + 1];
-    }
-  }
-
   void InsertAt(intptr_t idx, const T& value) {
     Resize(length() + 1);
     for (intptr_t i = length_ - 2; i >= idx; i--) {