[css-fonts-4] Follow up to override-color context

This is a follow-up to
w3c@da9c67d.
Colors are not resolved per-element, so variables shouldn't be, either.

Author: litherum

css-fonts-4/Overview.bs

@@ -6588,9 +6588,6 @@ Overriding a colors from a palette: The 'override-colors!!descriptor' descriptor
     the first key is used for the purposes of rendering. However, for serialization purposes, both
     key/value pairs are present.
 
-    Using CSS Variables is explicitly expected to be valid in the value of this descriptor.
-    CSS Variables are resolved in the context of the element to which the 'font-palette' property applies.
-
     Note: This means that using 'font-palette' with the same value on two different elements
     might result in different used palettes
     because the value of variables inside the ''@font-palette-values'' rule