Remove 3.7

[tianon]

3.7 goes out of any kind of support on October 1st. There will be one more security patch release of 3.7.x, after that, we can basically assume the 3.7 flavour of this image won't have any upstream releases to benefit from.

Honestly, the attack 3.7.28 will address is local, requires elevated privileges and is Windows-specific. So this image isn't really affected.

• @michaelklishin, Use load_definitions instead of management.load_definitions #430 (comment)

[michaelklishin]

@tianon if we wait for 3.7.28 to be produced and published, we'd have likely the last 3.7 release up on Docker Hub. Then we can merge this.

[michaelklishin]

A version with 3.7.28 has been published. Should we merge this @tianon @gerhard?

[tianon]

Once we get docker-library/official-images#8568 merged, I'll rebase and merge 👍

[tianon]

(Unless @gerhard objects to removing 3.7 before then -- we can always bring it back again if we need to)

[gerhard]

No objections @tianon.

RabbitMQ release series 3.7 reached end of General Support on 31 March 2020, which is what open source users care about, including the overwhelming majority that uses this Docker image.

With 3.7.28 out & merged, it's a good time to stop supporting 3.7 in this Docker image.

[tianon]

Ok, rebased, green, all is well. Let's do this. 😄