Remove a constructor that we can't test. (#340)

There are currently no paths that lead to it, and it has
a bug anyway; if a large enough value is passed into sec,
then we will overflow sec on the multiply.  Just remove it
since we can't reach the code anyway.

Signed-off-by: Chris Lalancette <clalancette@openrobotics.org>

rclcpp/include/rclcpp/time.hpp

@@ -62,10 +62,6 @@ public:
 private:
   rcl_time_point_value_t rcl_time_;
 
-  Time(std::uint32_t sec, std::uint32_t nanosec)
-  : rcl_time_(RCL_S_TO_NS(sec) + nanosec)
-  {}
-
   explicit Time(rcl_time_point_value_t && rcl_time)
   : rcl_time_(std::forward<decltype(rcl_time)>(rcl_time))
   {}