Merge bitcoindevkit/bdk#761: Remove redundant duplicated keys check

e2bf9734b16f5a0f419f1c1fc39c9773fd7e1128 Remove redundant duplicated keys check (Alekos Filini)

Pull request description:

  ### Description

  This check is redundant since it's already performed by miniscript (see https://docs.rs/miniscript/7.0.0/miniscript/miniscript/analyzable/enum.AnalysisError.html#variant.RepeatedPubkeys) and it was incorrectly failing on tr descriptors that contain duplicated keys across different taproot leaves

  Fixes #760

  ### Changelog notice

  ### Checklists

  #### All Submissions:

  * [x] I've signed all my commits
  * [x] I followed the [contribution guidelines](https://github.com/bitcoindevkit/bdk/blob/master/CONTRIBUTING.md)
  * [x] I ran `cargo fmt` and `cargo clippy` before committing

  #### Bugfixes:

  * [x] This pull request breaks the existing API
  * [x] I've added tests to reproduce the issue which are now passing
  * [x] I'm linking the issue being fixed by this PR

ACKs for top commit:
  danielabrozzoni:
    Code review ACK e2bf9734b16f5a0f419f1c1fc39c9773fd7e1128 - the code looks good to me, but I didn't test manually

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