remove reference to link in old book which breaks pod2onepage

doc/Language/101-basics.pod6

@@ -319,8 +319,7 @@ are passed in through the I<topic variable> C<$_>.
 
 You have seen blocks before: both the C<for> loop C<< -> $line { ... } >> and
 the C<if> statement worked on blocks.  A block is a self-contained piece of
-Perl 6 code with an optional signature (the C<< -> $line >> part).  See
-A<sec:signatures> for more information.
+Perl 6 code with an optional signature (the C<< -> $line >> part).
 
 The simplest way to sort the players by score would be C<@names.sort({
 %matches{$_} })>, which sorts by number of matches won. However Ana and Dave