Avoid unwanted line break in wxDataViewListModel::GetCount() docs.

Avoid unwanted line break in wxDataViewListModel::GetCount() docs.

Using "i.e." in the brief Doxygen comment makes it end it after the second
period and results in truncated brief description and an unwanted line break
in the full description.

Just avoid using periods for now inside the brief description. Maybe a better
solution could be found in the future.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@68519 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775