Merge bitcoindevkit/bdk#2192: [0.23.x] Backport #2190

Merge bitcoindevkit/bdk#2192: [0.23.x] Backport #2190

e9f78efdd4d422ba2d0ddec5fe25d51a05d0802a fix(ci): pin `rustls@0.23.39` to v0.23.26 (Luis Schwab)
add0ef02d0030cf6a07fa5c82e4ae6d56b8846df chore: remove unused `start-core.sh` script (Luis Schwab)

Pull request description:

  Backports #2190 to `release/chain-0.23.x`

  ## Changelog
  ```
  - Remove the unused `ci/start-core.sh` script
  - Pin rustls@0.23.39 to v0.23.26 for MSRV
  ```

ACKs for top commit:
  evanlinjin:
    ACK e9f78efdd4d422ba2d0ddec5fe25d51a05d0802a

Tree-SHA512: abc907fc458307afe6bfea72d8b0b1f2f2c2806eccbdd4a2de4e1e9573b6c6c11f7c89379dd5e285396cee9c6f3b24a947a7f04b3cbe346bcb28c4d6eaf20a2c