staging: hv: remove unneeded osd_schedule_callback

No one calls it anymore, so remove it.

Reviewed-By: Hank Janssen <hjanssen@microsoft.com>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: Timo Teräs <timo.teras@iki.fi>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>