Merge bitcoindevkit/bdk#1386: Remove TxBuilder allow_shrinking() and unneeded context...

096b8ef781b21e7da690b9ca2e4b326880d6ac0b fix(wallet): remove TxBuilder::allow_shrinking function and TxBuilderContext (Steve Myers)

Pull request description:

  ### Description

  Remove wallet::TxBuilder::allow_shrinking() and unneeded TxBuilder context param.

  Fixes #1374

  ### Notes to the reviewers

  The allow_shrinking function was the only one using the TxBuilder FeeBump context and it's useful to have CreateTx context  functions available for building FeeBump transactions, see updated tests.

  ### Changelog notice

  Changed

  - Removed TxBuilder::allow_shrinking() function.

  ### 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
  * [ ] I've added tests to reproduce the issue which are now passing
  * [x] I'm linking the issue being fixed by this PR

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Tree-SHA512: f4f05ce4cfaced9e61eebc0ebfe77a299fae13df4459fc26c90657297a1347a5d16f22b4e1c8b9b10458cfec80ca3b5d698eee11c7a560fd83f94a1ac7101a86