Remove non existing wxPG_COMPACTOR style from documentation.

No idea what was it supposed to do, but this style doesn't exist and never did
in the version included in wxWidgets, so simply remove it.

Closes #16264.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@76526 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775