Revert two commits related to Duration

Serious conceptual problems here, see
http://irclog.perlgeek.de/perl6/2013-12-01#i_7938521
for discussion.

This reverts commit 1735a46.
This reverts commit c32379e.

Author: Carl Masak

S32-setting-library/Temporal.pod

@@ -287,50 +287,6 @@ The C<Str> method returns a string of the form 'yyyy-mm-dd'.
     $d + 3                      # Date.new('2010-12-27')
     3  + $d                     # Date.new('2010-12-27')
 
-=head1 C<Interval>
-
-C<Interval> represents spans of time. They are similar to C<Duration>s except
-that you can specify spans of time beyond just seconds.
-
-    my $passed = Interval.new( :years(5), :months(0), :days(12),
-        :hours(10), :minutes(2), :seconds(0) );
-
-The named arguments form works similar to the C<DateTime> named arguments form,
-except for the pluralized argument names in C<Interval> objects.
-
-Un-specified arguments default to zero, so the above could more simply be
-written as
-
-    my $passed = Interval.new( :years(5), :days(12), :hours(10), :minutes(2) );
-
-An ISO 8601 Interval string is also permissable, with omitted fields defaulting
-to zero. The ISO 8601 version of the above would be either of the following:
-
-    my $passed = Interval.new("P5Y12DT102M");
-    my $passed = Interval.new("P0005-00-12T10:02:00");
-
-The C<"P[weeks]W"> form works as well. The following are equivalent:
-
-    my $weeks = Interval.new("P6W");
-    my $weeks = Interval.new("P42D");
-
-Fractions are allowed for the most granular value specified only.
-
-=head2 Accessor Methods
-
-The following methods on a C<Interval> object return a duration in that unit of
-time as either an C<Int> or a C<Rat>, whichever is narrower.
-
-    years
-    months  (assumes 30-day months)
-    weeks
-    days
-    hours
-    minutes
-    seconds
-
-The C<Str> method returns the interval as an valid ISO-8601 duration.
-
 =head1 FOOTNOTE
 
 The authors of the current rewrite want to mention, with thanks, the