update TODO

Author: odersky

compiler/src/dotty/tools/dotc/core/Flags.scala

@@ -18,10 +18,9 @@ object Flags {
   }
   type FlagSet = opaques.FlagSet
   def FlagSet(bits: Long): FlagSet = opaques.FlagSet(bits)
-  // DOTTY problem: would like to replace previous 2 lines with
+  // DOTTY TODO: replace previous 2 lines with
   //   export opaques.FlagSet
-  // but this makes `def FlagSet` in `opaques` ill-typed.
-
+  // once 0.17 is released and #6721 is in the bootstrap
 
   delegate FlagOps {