Remove implementation notes obsoleted by 2015.11

Tested with IRC evalbot Rakudo 2015.11.505.ge.52617.c.

doc/Language/control.pod

@@ -256,9 +256,6 @@ two differences C<unless> works the same as L<if>:
     my $c = 0; say (1, (unless 0 { $c += 42; 2; }), 3, $c); #-> says "1 2 3 42"
     my $c = 0; say (1, (unless 1 { $c += 42; 2; }), 3, $c); #-> says "1 3 0"
 
-Implementation note: Currently, Rakudo will say "1 Nil 3 0" for the last
-example because it is not caught up to this part of the design yet.
-
 =head3 X<with, orwith, without|control flow,with orwith without>
 
 The C<with> statement is like C<if> but tests for definedness rather than