Drivers: hv: vmbus: Remove unused extern declaration vmbus_ontimer()

Since commit 30fbee49 ("Staging: hv: vmbus: Get rid of the unused function vmbus_ontimer()")
this is not used anymore, so can remove it.
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Link: https://lore.kernel.org/r/20230725142108.27280-1-yuehaibing@huawei.comSigned-off-by: Wei Liu <wei.liu@kernel.org>

include/linux/hyperv.h

@@ -1239,9 +1239,6 @@ extern int vmbus_recvpacket_raw(struct vmbus_channel *channel,
 				     u32 *buffer_actual_len,
 				     u64 *requestid);
 
-
-extern void vmbus_ontimer(unsigned long data);
-
 /* Base driver object */
 struct hv_driver {
 	const char *name;