refactor: use types::KeychainKind where appropriate

[thunderbiscuit]

This small fix came up in my review of #971. I realized we used what looked like on the surface to be 2 versions of the KeychainKind type, one directly from bdk_wallet and one from our custom-written types.

This is not the case and they were both coming from our custom-written types, but the imports made this confusing and not obvious. This PR fixes that.

Documentation

• bdk_wallet
• bitcoin
• uniffi
• Other:

Checklists

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New Features:

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Bugfixes:

• This pull request breaks the existing API
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[reez]

ACK bb1b6fa

yeah this is a nice change/cleanup