Revert "Use "is default" for IO::Handle atttributes"

This reverts commit c63c57e.

Hopefully fix the problems in IO::String.

src/core/IO/Handle.pm

@@ -5,9 +5,9 @@ my class Proc { ... }
 my class IO::Handle {
     has $.path;
     has $!PIO;
-    has $.chomp is rw is default(True);
-    has $.nl-in is default(["\x0A", "\r\n"]);
-    has Str:D $.nl-out is rw is default("\n");
+    has $.chomp is rw = Bool::True;
+    has $.nl-in = ["\x0A", "\r\n"];
+    has Str:D $.nl-out is rw = "\n";
     has Str $.encoding;
     has Encoding::Decoder $!decoder;
     has Encoding::Encoder $!encoder;