common: remove core_log_to_last

[grom72]

• Minor fixes to core_log_va()
• Remove core_log_to_last() and keep only one way to use core_log_va() from core_log() (with new invisible level).

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This change is 

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 70.05%. Comparing base (6b911a6) to head (73aca9f). Report is 1 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #6030 +/- ## ======================================= Coverage 70.04% 70.05% ======================================= Files 133 133 Lines 19564 19563 -1 Branches 3263 3263 ======================================= Hits 13704 13704 + Misses 5860 5859 -1 ```