restoring to the 2 abstract functions with an updated count

references feedback from here w3c@e5290a2#commitcomment-36062322

Author: Adam Argyle

css-color-5/Overview.bs

@@ -35,10 +35,9 @@ Introduction {#intro}
 	like yellow and blue,
 	can have the same HSL lightness).
 
-	This module adds three functions:
+	This module adds two functions:
 	''color-mix'',
-	''color-contrast'' and
-	''color-adjust''.
+	''color-contrast''.
 
 	The perceptually uniform ``lch()`` colorspace
 	is used for mixing by default,