Eliminates useless X<> tag

tisonkun · tisonkun · commit 033880b1bc8d · 2018-04-17T09:22:58.000+08:00
diff --git a/doc/Type/utf8.pod6 b/doc/Type/utf8.pod6
@@ -3,7 +3,7 @@
 =TITLE class utf8
 
 =SUBTITLE Mutable uint8 buffer for utf8 binary data
-X<|utf, class>
+
     class utf8 does Blob[uint8] is repr('VMArray') {}
 
 A C<utf8> is a subtype of Blob which is specifically uint8 data for holding UTF-8
