Change wxLongLongFmtSpec to be a non-wide string.

As with other ANSI/Unicode unification changes, we choose to preserve
compatibility with the existing code using wxLongLongFmtSpec in ANSI build
and require people using it in Unicode build to change their code.

Closes #11372.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@62562 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775