HID: i2c-hid: remove orphaned member sleep_delay

This was introduced in commit 00b790ea ("HID: i2c-hid: Add a small
delay after sleep command for Raydium touchpanel") which has been
effectively reverted by commit 67b18dfb ("HID: i2c-hid: Remove
runtime power management").
Signed-off-by: You-Sheng Yang <vicamo.yang@canonical.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/hid/i2c-hid/i2c-hid-core.c

@@ -157,8 +157,6 @@ struct i2c_hid {
 
 	bool			irq_wake_enabled;
 	struct mutex		reset_lock;
-
-	unsigned long		sleep_delay;
 };
 
 static const struct i2c_hid_quirks {