Bluetooth: Controller: Remove HCI event definitions from hci.c

Delete all event definitions from hci.c since the code now
uses the ones in include/bluetooth/hci.h exclusively.
This is the fourth and last commit in a series that transitions
from the event structures in hci.c to the ones in hci.h.

Jira: ZEP-726

Change-Id: I625c2aecf759823a1cc73a3ea096564284fe8c52
Signed-off-by: Carles Cufi <carles.cufi@nordicsemi.no>