[avalanche] Simplify the processor test item providers by removing addToReconcile specialization

Summary:
Similar to D13061, the addToReconcile specialization is no longer needed and can be removed. There is no change in behavior.

Depends on D13061.

Test Plan:

ninja check-avalanche

Reviewers: #bitcoin_abc, sdulfari

Reviewed By: #bitcoin_abc, sdulfari

Differential Revision: https://reviews.bitcoinabc.org/D13062