ARM: at91: remove stale MAINTAINER file entries

Going through the entries of recently removed machine types,
I found these two that were removed a long time ago.

Acked-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Cc: Alexandre Belloni <alexandre.belloni@bootlin.com>
Cc: Claudiu Beznea <claudiu.beznea@microchip.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>