Links on Event Types & Payloads section go to api.github.com

## Description
There are several links on the Event Types & Payloads section that attempt to navigate to api.github.com. These should probably either be updated to go to the relevant section of our lively docs or removed altogether. 

For instance the repository webhooks link attempts to go to https://api.github.com/v3/repos/hooks/, but should probably either go to /github/hooks or not be a link.

## Details
/github/event-types--payloads