Revert "Alternate fix for JVM breakage to PR #4189"

bartolin++ figured out that it was actually missing deconts on the
JVM backend that caused problems.  So add them.

This reverts commit f627ccb

src/core.c/DateTime.pm6

@@ -173,34 +173,22 @@ my class DateTime does Dateish {
             %extra,
     --> DateTime:D) {
         self!oor("Month",$month,"1..12")
-#?if jvm
-          unless 1 <= $month <= 12;
-#?endif
-#?if !jvm
-          if nqp::islt_I($month,1) || nqp::isgt_I($month,12);
-#?endif
+          if nqp::islt_I(nqp::decont($month),1)
+          || nqp::isgt_I(nqp::decont($month),12);
+
         my $DIM := self!DAYS-IN-MONTH($year,$month);
         self!oor("Day",$day,"1..$DIM")
-#?if jvm
-          unless 1 <= $day <= $DIM;
-#?endif
-#?if !jvm
-          if nqp::islt_I($day,1) || nqp::isgt_I($day,$DIM);
-#?endif
+          if nqp::islt_I(nqp::decont($day),1)
+          || nqp::isgt_I(nqp::decont($day),$DIM);
+
         self!oor("Hour",$hour,"0..23")
-#?if jvm
-          unless 0 <= $hour <= 23;
-#?endif
-#?if !jvm
-          if nqp::islt_I($hour,0) || nqp::isgt_I($hour,23);
-#?endif
+          if nqp::islt_I(nqp::decont($hour),0)
+          || nqp::isgt_I(nqp::decont($hour),23);
+
         self!oor("Minute",$minute,"0..59")
-#?if jvm
-          unless 0 <= $minute <= 59;
-#?endif
-#?if !jvm
-          if nqp::islt_I($minute,0) || nqp::isgt_I($minute,59);
-#?endif
+          if nqp::islt_I(nqp::decont($minute),0)
+          || nqp::isgt_I(nqp::decont($minute),59);
+
         (^61).in-range($second,'Second'); # some weird semantics need this
 
         my $dt := nqp::eqaddr(self.WHAT,DateTime)