`MyIni.DeleteSection(section)` does not remove the section's keys

Description: `MyIni.DeleteSection` removes the section from the section list, then removes keys whose name equals the section name (`key.NameSegment.EqualsIgnoreCase(section)`) instead of whose section equals it (`key.SectionSegment`). The section's actual keys remain in the ini. Re-adding the section (via `Set`/`AddSection`) resurrects the stale keys, so "replace whole section" logic silently accumulates duplicates.

Real-world impact: PB scripts that store data by rewriting a section each save (`DeleteSection` + `Set` per key) keep every old key forever.

Repro (paste into any PB; the result is an echo, visible on the PB terminal immediately after compile):

public Program()
{
    var ini = new MyIni();
    ini.Set("Values", "100", "ValueA");
    ini.Set("Values", "200", "ValueB");

    ini.DeleteSection("Values");

    var keys = new List<MyIniKey>();
    ini.GetKeys("Values", keys);

    ini.Set("Values", "300", "ValueC");

    var sb = new StringBuilder();
    sb.AppendLine($"DeleteSection(\"Values\") left {keys.Count} of 2 keys behind:");
    foreach (var key in keys)
    {
        sb.AppendLine($"  {key}");
    }
    sb.AppendLine();
    sb.AppendLine("Expected after DeleteSection: section gone, 0 keys.");
    sb.AppendLine($"Actual ini after re-populating the section (stale keys are back):");
    sb.Append(ini.ToString());
    Echo(sb.ToString());
}

public void Main(string argument, UpdateType source)
{
}

public void Save()
{
}

Expected output: `left 0 of 2 keys behind`, final ini `[Values] 300=ValueC`.

Actual: `left 2 of 2 keys behind: Values/100, Values/200`, final ini contains `100=ValueA`, `200=ValueB` (stale) and `300=ValueC`.

Suggested fix: in `MyIni.DeleteSection`, `key.NameSegment` → `key.SectionSegment`.