Remove telemetry_sync_v5

[acmiyaguchi]

sync v5 was a mistake, as per bug 1410145. There is a surprising number of pings that are arriving on this doc version though (https://sql.telemetry.mozilla.org/queries/64998/source).

We should remove this table from the BigQuery dataset too, since it's causing telemetry.sync to alias to telemetry.sync_v5.

[whd]

CI is still failing on the third-party-modules change, for some reason.

Given the relatively high volume, I want somebody (@mreid-moz?) to make a policy decision that we can/should delete this table. We haven't sorted out #386 yet and probably won't for some time. In the current model, we will remove these tables in a mostly non-reversible fashion.

An alternative solution would be to special-case the sync ping unversioned view to point at v4. Absent any compelling reasons I prefer this approach, since it appears we're using a hard-coded view at the moment anyway.

[mreid-moz]

Either way, we need to fix the view to point to v4, so I sent mozilla/bigquery-etl#401.

I've asked for confirmation on deleting the data (as well as adding my understanding of the implications) in Bug 1572744#c4.

[acmiyaguchi]

Closing per https://bugzilla.mozilla.org/show_bug.cgi?id=1572744#c9