log: Remove GetAdjustedTime from IBD header progress estimation

Summary:

This is a "refactor" that shouldn't change behaviour, because the two times are most likely equal. A minimum of 5 outbound peers are needed to adjust the time. And if the time is adjusted, it will be by at most 70 minutes (DEFAULT_MAX_TIME_ADJUSTMENT). Thus, the progress estimate should differ by at most 7 blocks.

This is a backport of core#24033

Test Plan: ninja all check-all

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D12910