[ARM] remove drivers/acorn/char/defkeymap-l7200.c

The config option for building drivers/acorn/char/defkeymap-l7200.c is
not present since at least kernel 2.6.0.

Signed-off-by: Adrian Bunk <bunk@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>