Revert "Uploaded correct pic for agl-compositor-popup-screenshot"

This reverts commit eb8ce592.

The MR was merge by accident while being reviewed. The picture itself is
not incorrect, however, it does not follow the format of others pictures
related to agl-compositor.

Reverting this, while preparing a better MR.

Signed-off-by: Walter Lozano <walter.lozano@collabora.com>