Fix wxLocale::GetInfo() in C locale under Windows.

Fix wxLocale::GetInfo() in C locale under Windows.

Don't use LOCALE_USER_DEFAULT when the locale hadn't been changed because the
user default locale often (and maybe even always) is different from "C" locale
used by the CRT resulting in mismatch between the conventions used by
wxDateTime::Format(), which uses the CRT locale, and wxDateTime::Parse(),
which uses Windows format. Instead use the hard-coded values corresponding to
the "C" locale to ensure we use the same values as the CRT in this case.

This also reverts r73244 which was applies to make the unit tests pass before
this fix as it's not necessary any longer.

Closes #14918.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@73320 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775