Fix build with wxUSE_STD_STRIN == 0.

Remove a leftover occurrence of wxDEFINE_TEMPLATE_BOOL_VALUE(), this should
have been done in r76532.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@77490 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775