Remove declaration of unused function: void UpdatedTransaction(const uint256 &)

Summary: Backport of core PR10834

Test Plan:

make

Reviewers: #bitcoin_abc, deadalnix, jasonbcox

Reviewed By: #bitcoin_abc, jasonbcox

Subscribers: teamcity, schancel

Differential Revision: https://reviews.bitcoinabc.org/D2199