wallet: Avoid locking cs_wallet recursively

Summary:

wallet: GetLabelAddresses requires cs_wallet lock

No change in behavior, the lock is already held at call sites.

wallet: AddWalletDescriptor requires cs_wallet lock

No change in behavior, the lock is already held at call sites.

Also remove getLabelAddresses in wallet interface. This was added in D2886, but Bitcoin Core never had this function and it compiles fine without it.

This is a backport of core#19833

Test Plan:
debug and tsan build
ninja all check check-functional

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D14730