wallet: GetWalletTx requires cs_wallet lock

Summary:
PR description:

This change removes some unlock/lock and lock/lock cases regarding GetWalletTx and IsMine overloads.

This is a backport of core#19289 [1/3]
https://github.com/bitcoin/bitcoin/pull/19289/commits/a13cafc6c6998baedf3c5766259c21fcd763b99e

Test Plan:
With TSAN:
ninja all check-all

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D10095