Revert "Merge pull request #350 from Thiago4532/opaque-window-border"
Revert "Merge pull request #350 from Thiago4532/opaque-window-border"

This reverts commit dbe9c4f799fd826c199169d012c2d2687b210a7f, reversing
changes made to f6e4e278b54a8c37bfcd620debf4256cb59b875a.

A discussion of why, as well as a new way forward, in being discussed in

    https://github.com/xmonad/xmonad/issues/395

However, since we would like to release a new minor version soon-ish,
it's better to revert this for now.

xmonad/xmonad