Fix excessive height of wxSlider with labels but no ticks in wxMSW.

We shouldn't add the label height to the control best height as the labels are
positioned at the same vertical level as the main part of the control.

See #16604.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_3_0_BRANCH@77984 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775