Delete a stale issue that has already been addressed (w3c#292)

Author: nainar

css-typed-om/Overview.bs

@@ -295,9 +295,6 @@ After execution, the value of <code>opacity</code> is 1 ('opacity' is range-rest
 and the value of <code>zIndex</code> is 15 ('z-index' is rounded to an integer value).
 </div>
 
-Issue(140): where does a description of parsing values go? For example, where do we indicate that
-			 calc(4 + 8) will create a {{CSSNumberValue}} with a value of 12?
-
 {{CSSLengthValue}} objects {#lengthvalue-objects}
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