drivers/rtc/rtc-max6900.c: remove empty function

After the switch to devm_* functions and the removal of
rtc_device_unregister(), the 'remove' function does not do anything.
Delete it.

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Cc: Dale Farnsworth <dale@farnsworth.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>