Fix some obsolete documentation in CostFunction::Evaluate

Change-Id: I1d7ee5c596fbf6a4d886dce5b989c8eb18af2dce

include/ceres/cost_function.h

diff --git a/include/ceres/cost_function.h b/include/ceres/cost_function.h
index 45292ec..fe8fc07 100644
--- a/include/ceres/cost_function.h
+++ b/include/ceres/cost_function.h
@@ -106,8 +106,7 @@
   // the constraints, then returning false whenever the constraints
   // are not satisfied will prevent the solver from moving into the
   // infeasible region. This is not a very sophisticated mechanism for
-  // enforcing constraints, but is often good enough for things like
-  // non-negativity constraints.
+  // enforcing constraints, but is often good enough.
   //
   // Note that it is important that the initial values of the
   // parameter block must be feasible, otherwise the solver will