Revert "wpe: Properly respect LIBGL_ALWAYS_SOFTWARE"

Revert "wpe: Properly respect LIBGL_ALWAYS_SOFTWARE"

This causes issues I didn't see:
     https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/2252#note_927633

Let's just tell people to use capsfilter to force software rendering in
`wpesrc` for now.

The intent was to allow forcing it easily in playbin2 for the CI, but
we will do it some other way and see when time comes.

This reverts commit 9415106b029e5469ca28d882dc46ecc38786d4c9.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/2273>