rtc: Remove unused RTC_DEVICE_NAME_SIZE

The last usage was removed in 5c82a6ae0 when rtc_device.name
was removed

Signed-off-by: Cole Robinson <crobinso@redhat.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>

include/linux/rtc.h

@@ -87,7 +87,6 @@ struct rtc_class_ops {
 	int (*set_offset)(struct device *, long offset);
 };
 
-#define RTC_DEVICE_NAME_SIZE 20
 typedef struct rtc_task {
 	void (*func)(void *private_data);
 	void *private_data;