Mark a subtype rule as redundant, in a TODO comment

Author: eernstg

specification/dartLangSpec.tex

@@ -21969,6 +21969,8 @@ \subsection{Subtypes}
     \RuleRaw{\SrnRightTop}{%
       T \in \{\code{Object?}, \DYNAMIC, \VOID\}}{S}{T}
     % ------------------------------------------------ Right Object
+    % TODO(eernst): Comment out this rule as redundant and
+    % renumber, it is an instance of \SrnRightFutureOrB.
     \RuleRaw{\SrnRightObjectFour}{%
       \mbox{$S$ is an interface type or \FUNCTION}}{S}{\code{Object}}
     % ------------------------------------------------ Left Null 2