S04: Fix pre-GLR-ism

isn't it wonderful how much simpler this passage becomes through the GLR?

S04-control.pod

@@ -8,8 +8,8 @@ Synopsis 4: Blocks and Statements
 
     Created: 19 Aug 2004
 
-    Last Modified: 8 Aug 2015
-    Version: 139
+    Last Modified: 19 Sep 2015
+    Version: 140
 
 This document summarizes Apocalypse 4, which covers the block and
 statement syntax of Perl.
@@ -383,16 +383,8 @@ There is no longer a C<continue> block.  Instead, use a C<NEXT> block within
 the body of the loop.  See below.
 
 The value of a loop statement is the list of values from each iteration.
-Each iteration's value is returned as a single "argument" object.  See
-L<S02> for a long definition of argument, but in short, it's either an
-ordinary object or a parcel containing multiple values.
-
-Normal flat list context ignores parcel boundaries and flattens the list.
-
-Iterations that return C<()> (such as by calling C<next> with no extra
-return arguments) return that C<()> as the next value, which will therefore
-disappear when interpolated in flat context, but will interpolate an empty
-C<List> into slice context.
+Each iteration's value is returned as a single object, only C<Slip>s flatten
+into the return list.
 
 For finer-grained control of which iterations return values, use C<gather>
 and C<take>.