Correct docs for Dateish.[days-in-month|is-leap-year]

The argument-taking candidates of the two methods were never part of
the Perl 6 specification and have now been removed[^1] from Rakudo.

[1] rakudo/rakudo@6aab641

Author: zoffixznet

doc/Type/Dateish.pod6

@@ -71,13 +71,12 @@ invocant as its only argument.
 
 Defined as:
 
-    method is-leap-year($year = self.year) returns Bool:D
+    method is-leap-year() returns Bool:D
 
-Returns C<True> if C<$year> is a leap year. Can be called as a class method
-if the year is provided.
+Returns C<True> if the year of the Dateish object is a leap year.
 
-    say Dateish.is-leap-year(2016);           # True
-    say Date.new("1900-01-01").is-leap-year;  # False
+    say DateTime.new(:year<2016>).is-leap-year; # True
+    say Date.new("1900-01-01").is-leap-year;    # False
 
 =head2 method day-of-month
 
@@ -119,12 +118,10 @@ Defined as:
 
     method days-in-month(Dateish:D:) returns Int:D
 
-Returns the number of days in a month, where year and month default to that
-of the invocant. If both year and month are provided, it can be called as
-a class method.
+Returns the number of days in the month represented by the Dateish object:
 
-    say Date.new("2016-01-02").days-in-month;  # 31
-    say Dateish.days-in-month(2016, 1);        # 31
+    say Date.new("2016-01-02").days-in-month;                # 31
+    say DateTime.new(:year<10000>, :month<2>).days-in-month; # 29
 
 =head2 method week