doc: only U+FEFF is a byte-order mark; U+FFFE is not

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/9103046

doc/go1.1.html

@@ -272,10 +272,10 @@ values.
 </p>
 
 <p>
-The Unicode byte order marks U+FFFE and U+FEFF, encoded in UTF-8, are now permitted as the first
+The Unicode byte order mark U+FEFF, encoded in UTF-8, is now permitted as the first
 character of a Go source file.
-Even though their appearance in the byte-order-free UTF-8 encoding is clearly unnecessary,
-some editors add them as a kind of "magic number" identifying a UTF-8 encoded file.
+Even though its appearance in the byte-order-free UTF-8 encoding is clearly unnecessary,
+some editors add the mark as a kind of "magic number" identifying a UTF-8 encoded file.
 </p>
 
 <p>