nghttpx: Remove unused function declaration

src/shrpx_live_check.h

@@ -56,6 +56,7 @@ public:
 
   int initiate_connection();
 
+  // Schedules next connection attempt
   void schedule();
 
   // Low level I/O operation callback; they are called from do_read()
@@ -67,8 +68,6 @@ public:
   int do_read();
   int do_write();
 
-  void signal_write();
-
 private:
   Connection conn_;
   std::mt19937 &gen_;