Use wxPENSTYLE_{SOLID,TRANSPARENT} instead of deprecated versions in the docs.

Don't push people to use the deprecated wxSOLID and wxTRANSPARENT.

Closes #15775.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@75409 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775