Get rid of BindWallet

Summary:
CWalletTx initialization has been fixed so it's no longer necessary to change
which wallet a transaction is bound to.

This concludes backport of Core PR9381 [5/5]
https://github.com/bitcoin/bitcoin/pull/9381/commits/28b112e9bd3fd1181c0720306051ba7efca8b436
Depends on D9077

Test Plan: ninja all check-all

Reviewers: #bitcoin_abc, majcosta

Reviewed By: #bitcoin_abc, majcosta

Differential Revision: https://reviews.bitcoinabc.org/D9078