[housekeeping] Reorganise github labels

[carlosjeurissen]

The labels can use some cleanup and structure. Currently we have:
agenda, bug, Chrome: follow-up, discussion, documentation, duplicate, enhancement, future topics, good first issue, help wanted, inconsistency, invalid, question, spec clarification, task, topic: automated testing, topic: csp, topic: remote code, topic: secureStorage, topic: service worker, wontfix

My proposal is to start with removing the following unused labels:
bug
duplicate
"help wanted"
wontfix

And start prefixing similar labels to increase structure. Starting with
api: someApiName labels
These labels are used for specific APIs, like secureStorage, action.

Then we have the status labels. Which can include:
status: needs-discussion, status: consensus-reached, status: widely-implemented and status: needs-mv-upgrade
Related issue: #205

This issue is created to start the discussion on how we can better organise the community labels.

[Rob--W]

I've removed "bug" and "help wanted" since they're clearly not useful for this repo.

"duplicate" and "wontfix" are potentially meaningful, but since there are no existing issues with the label, and the there is no real value in tracking these statuses separately, I've just removed it.

[xeenon]

Lets use #244 for this going forward.