[core] Removed unused constructorupstream/tvn-test-ci-time-out

Not in use at the moment, was causing a compiler error on
Apple LLVM version 8.0.0 (clang-800.0.42.1).

```
src/mbgl/sprite/sprite_loader.cpp:25:11: error: call to constructor of
'Actor<mbgl::SpriteLoaderWorker>' is ambiguous
```

1 files changed, 0 insertions, 8 deletions

diff --git a/include/mbgl/actor/actor.hpp b/include/mbgl/actor/actor.hpp
index 74d5a66285..6610421eb5 100644
--- a/include/mbgl/actor/actor.hpp
+++ b/include/mbgl/actor/actor.hpp
@@ -57,14 +57,6 @@ public:
               object(self(), std::forward<Args>(args_)...) {
     }
 
-    // Enabled for plain Objects
-    template <typename U = Object, class... Args,
-            typename std::enable_if<!std::is_constructible<U, ActorRef<Object>, Args...>::value>::type...>
-    Actor(Scheduler& scheduler, Args&&... args_)
-            : mailbox(std::make_shared<Mailbox>(scheduler)),
-              object(std::forward<Args>(args_)...) {
-    }
-
     ~Actor() {
         mailbox->close();
     }