[io grant] Remove type constraint in IO::Spec::Cygwin.canonpath

To align its interface with all the other ::Spe::*.canonpaths

src/core/IO/Spec/Cygwin.pm

@@ -1,6 +1,6 @@
 my class IO::Spec::Cygwin is IO::Spec::Unix {
 
-    method canonpath (Cool:D $patharg, :$parent) {
+    method canonpath ($patharg, :$parent) {
         my $path = $patharg.Str;
         $path.=subst(:g, '\\', '/');