staging: MAINTAINERS: remove NCP filesystem entry

The ncp filesystem got removed in November of 2017, yet the MAINTAINERS
entry persisted.  Remove that now.

Reported-by: Joe Perches <joe@perches.com>
Cc: Petr Vandrovec <petr@vandrovec.name>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>