Rephrase background information about media types

Since the `speech` media type has now also been deprecated (see w3c#1751 (comment)), this clarifies that the CSS properties defined for CSS Speech Module apply to all media types, and that they cannot be scoped in the way that was described

Author: patrickhlauke

css-speech-1/Overview.bs

@@ -63,22 +63,18 @@ Background information, CSS 2.1</h2>
 	The CSS Speech module is a re-work of the informative
 	<a href="https://www.w3.org/TR/CSS2/aural.html">CSS2.1 Aural appendix</a>,
 	within which the ''aural'' media type was described,
-	but also deprecated (in favor of the ''speech'' media type).
-	Although the [[!CSS2]] specification reserves the ''speech'' media type,
-	it doesn't actually define the corresponding properties.
-	The Speech module describes the CSS properties
-	that apply to the ''speech'' media type,
+	but also deprecated (in favor of the ''speech'' media type, which has now
+	also been deprecated).
+	Although the [[!CSS2]] specification reserved the ''speech'' media type,
+	it didn't actually define the corresponding properties.
+	The Speech module describes the CSS properties that apply to speech output,
 	and defines a new “box” model specifically for the aural dimension.
 
-	Content creators can conditionally include
-	CSS properties dedicated to user agents
-	with text to speech synthesis capabilities,
-	by specifying the ''speech'' media type
-	via the <code>media</code> attribute of the <{link}> element,
-	or with the ''@media'' at-rule,
-	or within an ''@import'' statement.
-	When styles are authored within the scope of such conditional statements,
-	they are ignored by user agents that do not support the Speech module.
+	Content creators can include CSS properties for user agents with
+	text to speech synthesis capabilities for any media type - though
+	generally, they will only make sense for ''all'' and ''screen''.
+	These styles are simply ignored by user agents that do not support
+	the Speech module.
 
 <h2 id="ssml-rel">
 Relationship with SSML</h2>