Remove Collection, Collections and clean up List/Set/Queue implementations of retain/remove.

pkg/yaml/lib/parser.dart

Index: pkg/yaml/lib/parser.dart
diff --git a/pkg/yaml/lib/parser.dart b/pkg/yaml/lib/parser.dart
index c84f3741d94ae3c92edb6872552b336b7ca9ef3e..9621b135d044ed23a3f0832437897fade114d047 100644
--- a/pkg/yaml/lib/parser.dart
+++ b/pkg/yaml/lib/parser.dart
@@ -1119,7 +1119,7 @@ class _Parser {
   });
 
   // 138
-  Collection<_Node> ns_s_flowSeqEntries(int indent, int ctx) {
+  Iterable<_Node> ns_s_flowSeqEntries(int indent, int ctx) {
     var first = ns_flowSeqEntry(indent, ctx);
     if (!truth(first)) return new Queue<_Node>();
     zeroOrOne(() => s_separate(indent, ctx));