Update README.md (thirdparty)

[aismann]

Describe your changes

Text adapted: DragonBones version (For new release strategy, should remove in release +2 aka 2.3) Replacing the GUI takes too much effort. So stay it there for internal using.

Issue ticket number and link

Checklist before requesting a review

For each PR

• [ ] Add Copyright if it missed:
  • "Copyright (c) 2019-present Axmol Engine contributors (see AUTHORS.md)."

• [x] I have performed a self-review of my code.

  Optional:

  • [ ] I have checked readme and add important infos to this PR.
  • [ ] I have added/adapted some tests too.

For core/new feature PR

• [ ] I have checked readme and add important infos to this PR.
• [ ] I have added thorough tests.

[halx99]

I think just mark deprecated, don't specify explicit remove release is better