remove discussion about falling back to plain DNS on timeout

doc/arm/Bv9ARM-book.xml

@@ -8963,18 +8963,7 @@ avoid-v6-udp-ports { 40000; range 50000 60000; };
 		  this has the greatest chance of success on the first try.
 		</para>
 		<para>
-		  If the initial response times out, <command>named</command>
-		  will try again with plain DNS, and if that is successful,
-		  it will be taken as evidence that the server does not
-		  support EDNS. After enough failures using EDNS and
-		  successes using plain DNS, <command>named</command>
-		  will default to plain DNS for future communications
-		  with that server.  (Periodically, <command>named</command>
-		  will send an EDNS query to see if the situation has
-		  improved.)
-		</para>
-		<para>
-		  However, if the initial query is successful with
+		  If the initial query is successful with
 		  EDNS advertising a buffer size of 512, then
 		  <command>named</command> will advertise progressively
 		  larger buffer sizes on successive queries, until