staging: rtl8723au: Remove useless static functions

This patch removes the static functions bthci_CmdSetEventFilter,
bthci_CmdReadRSSI and bthci_CmdHostNumberOfCompletedPackets, since their
body only consists of 'return HCI_STATUS_SUCCESS'.

Signed-off-by: Roberta Dobrescu <roberta.dobrescu@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>