[css-fonts-4] palette-mix() grammar requires color-interpolation-method, so remove leftover prose defining what to do if it is omitted w3c#8922

Author: svgeesus

css-fonts-4/Overview.bs

@@ -7287,9 +7287,6 @@ With the <code>palette-mix()</code> function defined as follows:
 		For each palette color, the interpolation follows
 		the rules of the <<color-mix()>> function.
 
-		When not specified otherwise the <<color-interpolation-method>> is
-		<code>in ''oklab''</code> as recommended by [[css-color-5#interpolation-space]].
-
 		Percentages are normalized according to [[css-color-5#color-mix-percent-norm]].
 </dl>