Remove legacy attributes, add supported_branches and consistently name update.module's XML fixtures

This is converted to an MR, tests updated and the legacy attributes removed. I am not sure what is meant in the title for "add supported branches" So, setting to NR to get some feedback.

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Not sure how to best test this one but the changes appear fine replacing with 8.0 versions

Committed and pushed 82d325ee79 to 11.x and 5ed786fdcc to 10.3.x. Thanks!

This was not a clean cherry-pcik to 10.2.x so left on 10.3.x and 11.x. Fingers-crossed we don;t have a security issue in private that makes changes to these tests.

Automatically closed - issue fixed for 2 weeks with no activity.