[css-properties-values-api] Remove reference to issue w3c#118. (w3c#874)

This is resolved now.

Author: andruud

css-properties-values-api/Overview.bs

@@ -712,8 +712,6 @@ Note: In other words, for the purpose of determining whether a value is
 supported by a given custom property, the type registered for the custom property is
 ignored and any value consisting of at least one token is considered valid.
 
-Issue(118): should @supports pay attention to type when considering custom properties?
-
 Relative URLs {#relative-urls}
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