Simplify HAL protos

* It's the HciHal, so HCI on functions and structs is redundant.
* FetchXYZ returns a stream, so rename to StreamXYZ
* Event & Commands are less about packets, so drop packet from the
struct names

Bug: 171749953
Tag: #gd-refactor
Test: gd/cert/run --rhost
Change-Id: I62fb098ee6a5a4805ad0667101c7de5a3368c4f2