Remove outdated info about custom skins
Remove outdated info about custom skins

It has been marked outdated for several years. Since it appears on the repo home
page, it makes the project feel unmaintained.

Signed-off-by: J. Ryan Stinnett <91e4c98f79b38ce04c052c188926e2d9ae2a3b28@gmail.com>

matrix-org/matrix-react-sdk,matrix-org/matrix-react-sdk,matrix-org/matrix-react-sdk,matrix-org/matrix-react-sdk,matrix-org/matrix-react-sdk,matrix-org/matrix-react-sdk