[backport#16224 5/5] util: Cleanup translation.h

Summary:
This concludes backport of Core PR16224 - part 5 of 5

Depends on D7998
Commit https://github.com/bitcoin/bitcoin/pull/16224/commits/18bd83b1fee2eb47ed4ad05c91f2d6cc311fc9ad

Test Plan: ninja && ninja check

Reviewers: O1 Bitcoin ABC, #bitcoin_abc, deadalnix

Reviewed By: O1 Bitcoin ABC, #bitcoin_abc, deadalnix

Subscribers: deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D7999