[css-values-4] Remove the older text about contexts; the new stuff is better imo. #11204

Author: tabatkins

css-values-4/Overview.bs

@@ -4340,22 +4340,6 @@ Type Checking</h3>
 	and to make division-by-zero detectable at parse time.
 	This version now relaxes those restrictions.
 
-	[=Calculations=] are evaluated in terms of some "context",
-	depending on where they are placed,
-	which determines how units are resolved,
-	how percentages are treated,
-	etc.
-	By default, this context is defined by the property/descriptor/etc
-	that the calculation is being used in.
-	Functions can define a different context
-	for their contained values.
-	(For example, ''media-progress()'' evaluates its [=calculations=]
-	in the context of the [=media feature=] it mentions.)
-	Directly nested [=math functions=]
-	(forming a larger [=calculation tree=])
-	always use the context of their top-most [=math function=],
-	so the entire [=calculation tree=] is consistent.
-
 	<div algorithm>
 		To <dfn>determine the type of a [=calculation=]</dfn>: