No real changes, just make some wxSlider members local variables.

No real changes, just make some wxSlider members local variables.

wxMSW wxSlider implementation stored the min and max labels widths as fields
of wxSlider object for some reason even though they were only used in one of
its methods (and can be easily computed anyhow).

Make them simple local variables instead and also rename an existing local
variable which started conflicting with their new names.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@68229 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775