Revert "Make "my $a of Array of Int" work (for typechecks at lowest l…

…evel)"

This should already work for multilevel typechecks, so we shouldn't normalize
the type to the lowest level.

This reverts commit 2857585.

src/core/Variable.pm

@@ -69,7 +69,7 @@ multi trait_mod:<of>(Variable:D $v, Mu:U $of ) {
         $var,
         $what.HOW.mixin_base($what),
         '$!descriptor'
-    ).set_of($of.HOW.mixin_base($of));
+    ).set_of(nqp::decont($of));
 }
 
 # phaser traits