Remove logheader callback feature; keep Kanta-colored extra string in default header

tests/test_logging.py

@@ -80,30 +80,6 @@ def test_log_change_appends_extra_string(capsys):
     assert f"{_TARGET}mydb.db{_RESET}" in captured.err
 
 
-def test_log_change_headerfmt_replaces_header(capsys):
-    kanta_logger = logging.getLogger("kanta")
-    kanta_logger.handlers.clear()
-    configure_logging()
-    log_change(
-        "update",
-        {},
-        headerfmt=lambda action, user, extra: f"CUSTOM {action} {extra}",
-        extra="7",
-    )
-    captured = capsys.readouterr()
-    assert "CUSTOM update 7" in captured.err
-
-
-def test_log_change_headerfmt_none_falls_back(capsys):
-    kanta_logger = logging.getLogger("kanta")
-    kanta_logger.handlers.clear()
-    configure_logging()
-    log_change("update", {}, user="alice", headerfmt=lambda *args: None)
-    captured = capsys.readouterr()
-    assert "update" in captured.err
-    assert "alice" in captured.err
-
-
 def test_log_change_log_diff_false(capsys):
     kanta_logger = logging.getLogger("kanta")
     kanta_logger.handlers.clear()