rtc: remove rtc_class_ops.read_callback

Since commit 416f0e80 ("RTC: sa1100: Update the sa1100 RTC driver."),
the last user of .read_callback is gone. It has been 8 years and now new
user appeared. Simply remove it.
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

drivers/rtc/dev.c

@@ -178,11 +178,6 @@ rtc_dev_read(struct file *file, char __user *buf, size_t count, loff_t *ppos)
 	remove_wait_queue(&rtc->irq_queue, &wait);
 
 	if (ret == 0) {
-		/* Check for any data updates */
-		if (rtc->ops->read_callback)
-			data = rtc->ops->read_callback(rtc->dev.parent,
-						       data);
-
 		if (sizeof(int) != sizeof(long) &&
 		    count == sizeof(unsigned int))
 			ret = put_user(data, (unsigned int __user *)buf) ?:

include/linux/rtc.h

@@ -67,7 +67,7 @@ extern struct class *rtc_class;
  *
  * The (current) exceptions are mostly filesystem hooks:
  *   - the proc() hook for procfs
- *   - non-ioctl() chardev hooks:  open(), release(), read_callback()
+ *   - non-ioctl() chardev hooks:  open(), release()
  *
  * REVISIT those periodic irq calls *do* have ops_lock when they're
  * issued through ioctl() ...
@@ -81,7 +81,6 @@ struct rtc_class_ops {
 	int (*proc)(struct device *, struct seq_file *);
 	int (*set_mmss64)(struct device *, time64_t secs);
 	int (*set_mmss)(struct device *, unsigned long secs);
-	int (*read_callback)(struct device *, int data);
 	int (*alarm_irq_enable)(struct device *, unsigned int enabled);
 	int (*read_offset)(struct device *, long *offset);
 	int (*set_offset)(struct device *, long offset);