ci: Build Arm64 on Travis without functional tests #20072

The Travis Arm64 env is a pretty big PITA for quite a while now. It simply seems to time out due to a lack of resources as far as I can tell from my research into the matter.

I have reported the issue in August and received no response: https://travis-ci.community/t/arm64-failing-without-message/9775. Others have complained about similar issues with Arm64 over the past year. The explanation for this is probably that this env is still considered to be in beta: https://docs.travis-ci.com/user/multi-cpu-architectures.

Considering the high frequency of failures (I didn't run any numbers, just based on my personal observations) and the beta status I would suggest that we shorten the runtime by removing part of the test suite until the env is more stable. I would suggest removing functional tests since it should help for sure but maybe there are other ideas.

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Conflicts

Reviewers, this pull request conflicts with the following ones:

• #20073 ([DO NOT MERGE] ci: Print TRAVIS_COMMIT_RANGE before fail by hebasto)

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ACK 33df8d46bb4b6daca91db208d3d1629d3c1e500c

I think we haven't seen failures in the arm functional tests that haven't been reproduced on other architectures, so it seems low risk removing them.