Remove Redshift mention from the list of managed Postgres backends

[Taragolis]

Redshift is mentioned as managed Postgres but is far away from the reality better to say it is product based on very old Postgres (something like 8.4) or even maybe only use Postgres protocol nowadays, difficult to say because it is cloud only proprietarily product.

Anyway there is small chance that end users might run Airflow by use Redshift as backend DB, so better remove from documentation fir prevent any confusion and misleading.

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[hussein-awala]

I agree, AWS used Postgres when they created Redshift, but I don't think it's the case today.

[potiuk]

Agree. This is "Redshift" and if people will use it at "Postgres Metadata" - weird things will happen. Like airlfow will sort-of works, which is worst outcome.