RootCanal: Move packets/hci/hci_packets.pdl -> packets/hci_packets.pdl

The hci/ subfolder was required with bluetooth_packetgen to generate
the module with the correct namespace; that is no longer the case
with pdlc

Bug: 279665786
Test: m root-canal
Change-Id: I0bceedb3e6ad39fe6ffbd00e05f6a935de94c120