Staging: hv: vmbus: Get rid of the unused wrapper - vmbus_onchannel_event()

Now, get rid of the unused wrapper - vmbus_onchannel_event().

Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: Abhishek Kane <v-abkane@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>