Temporarily remove BBAI 64 workflow

[acostach]

This device-type can not be built anymore because
the upstream beagleboard git repository has added
Anubis, which makes fetching of sources impossible from Yocto builds.

We've asked for a github mirror from the upstream maintainer. Until that becomes available, let's remove the workflow for this device-type to unblock merging of PRs.

Change-type: patch

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Contributor checklist

• Changes have been tested
  • Covered in automated test suite
  • Manual test case recorded
• Change-type present on at least one commit
• Signed-off-by is present
• The PR complies with the Open Embedded Commit Patch Message Guidelines

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  • 'Approve' if this change would be acceptable in the codebase (even if there are minor or cosmetic tweaks that could be improved).
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  • 'Comment' if you don't feel you have enough information to decide either way (e.g. if you have major questions, or you don't understand the context of the change sufficiently to fully review yourself, but want to make a comment)

[alexgg]

We have now amended the BB repository - leaving as draft until we confirm it all works.