wallet] remove nLastResend logic

Summary:
remove nLastResend logic, which is used to ensure rebroadcast doesn't happen again if no new block has been mined (makes sense in 10-15 min period, but not necessary for 12-36 hour period). 1

This is a backport of Core PR18895 [1/3]
https://github.com/bitcoin/bitcoin/pull/18895/commits/d16006960443c2efe37c896e46edae9dca86c57d

Depends on D9027

Test Plan: ninja all check-all

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D9023