[wallet] Don't rewrite accounting entries when reordering wallet transactions and remove WriteAccountingEntry()

Summary:
Accounting entries are deprecated. Don't rewrite them to the wallet
database when re-ordering transactions.

Also remove unused function.

Partial backport of Core PR13825
https://github.com/bitcoin/bitcoin/pull/13825/commits/3f248a873f941cbcc4d0c24021edcd11e927da98
https://github.com/bitcoin/bitcoin/pull/13825/commits/f992f7fa3eb1438cb01d35af699954ef6f79438a

Depends on D5413

Test Plan:

ninja check
test_runner.py wallet_*

Reviewers: O1 Bitcoin ABC, #bitcoin_abc, Fabien

Reviewed By: O1 Bitcoin ABC, #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D5414