s/setCallback_/setCallback/ for detail::State

Summary: This isn't really an internal-to-this-class method. :-/

Test Plan: builds

Reviewed By: hannesr@fb.com

Subscribers: jsedgwick, net-systems@, fugalh, exa

FB internal diff: D1412008

folly/wangle/Future-inl.h

@@ -59,7 +59,7 @@ template <class T>
 template <class F>
 void Future<T>::setCallback_(F&& func) {
   throwIfInvalid();
-  state_->setCallback_(std::move(func));
+  state_->setCallback(std::move(func));
   state_ = nullptr;
 }
 

folly/wangle/detail/State.h

@@ -47,9 +47,9 @@ class State {
   }
 
   template <typename F>
-  void setCallback_(F func) {
+  void setCallback(F func) {
     if (callback_) {
-      throw std::logic_error("setCallback_ called twice");
+      throw std::logic_error("setCallback called twice");
     }
 
     callback_ = std::move(func);