Bluetooth: Fix Remove Device to wait for HCI before sending cmd_complete

This patch updates the Remove Device mgmt command handler to use a
hci_request to wait for HCI command completion before notifying user
space of the mgmt command completion. This way we ensure that once the
mgmt command returns all HCI commands triggered by it have also
completed.

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>