Staging: hv: vmbus: Get rid of hv_cb_utils[] and other unneeded code

Now that the transformation of the util driver is complete,
get rid of hv_cb_utils[] and other unneeded code.

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