[Version-unspecific] Refactor TryAddTxOutItem to return an error value only (like UnSafeAddTxOutItem), no bool value #check-lint-warning

[Version-unspecific]

Intended to close #1589
'TryAddTxOutItem can be refactored to only return an error value (like UnSafeAddTxOutItem) rather than the confusing/ambiguous (bool, error) values'.

(Includes the removal of unreachable (dead) code that could only be reached if the error were nil and the bool were false.)

---

2024-05-21 update:

Following #1589 (comment 1913435619) ,
hardfork label added for the greater speed of reviewing if rewritten to only affect post-hard-fork versions.