wireless-regdb: Update keys and maintainer information

As announced [1], I am taking over maintainership of the wireless
regulatory database.

Make it official by replacing the key and certificate, and updating
maintainership information in various places.

[1] https://lore.kernel.org/all/CAGb2v657baNMPKU3QADijx7hZa=GUcSv2LEDdn6N=QQaFX8r-g@mail.gmail.com/

Signed-off-by: Chen-Yu Tsai <wens@kernel.org>
Signed-off-by: Seth Forshee <sforshee@kernel.org>