hw/escc: Drop duplicate definition of 'disabled' property

Drop a duplicate definition of the 'disabled' property from
the escc qdev property list: this redefinition is currently
effectively ignored but will become an error. (The duplication
was inadvertently introduced in 2009 in commit ec02f7de.)

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Acked-by: Andreas Färber <afaerber@suse.de>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>