Fix up from #12210: Excel without UIA enabled: again allow typing and editing in cells (#12321)
Fixes #12303
After merging of pr #12210 editing cells in Excel without UIA enabled became im possible as NVDA did not report / track focus had ented the Cell Edit control.
This was due to the EXCEL6 window accidentally being marked as having a good UIA implementation. This was testing code left over from the early implementation of #12210.
Description of how this pull request fixes the issue:
Remove EXCEL6 from the good UIA windows list.
Also ensure that MSAA focus events on this window are ignored when using Excel with UIA enabled, as Excel will fire its own UIA focus event on an edit control within the active cell.