message: remove outdated CI badges
diff: # Miri
  [![Actions build status][actions-badge]][actions-url]
  -[![Travis build status](https://travis-ci.com/rust-lang/miri.svg?branch=master)](https://travis-ci.com/rust-lang/miri)
  -[![Appveyor Windows build status](https://ci.appveyor.com/api/projects/status/github/rust-lang/miri?svg=true)](https://ci.appveyor.com/project/rust-lang-libs/miri)
  [actions-badge]: https://github.com/rust-lang/miri/workflows/CI/badge.svg?branch=master
  [actions-url]: https://github.com/rust-lang/miri/actions
  