Consider removing Aurora from normalized_channels

[fbertsch]

This channel has been deprecated awhile, and the bit of data that comes in just has to be filtered out if we e.g. group on channel.

[fbertsch]

Bucketing into other seems acceptable.

[jklukas]

Do you have reference on when this was deprecated? How many pings do we have coming in with it? Do we have a significant amount of historical data that legitimately has this channel?

My primary concern here is that we're introducing an artificial cliff for historical analyses where aurora disappears. Will that be confusing in analysis?

[fbertsch]

It's been three years: https://hacks.mozilla.org/2017/04/simplifying-firefox-release-channels/

For those other questions, we'll have to run some queries to find out. I haven't seen an analysis that uses aurora for many years. Reaching out to DS seems relevant.