Mark a team as unhealthy when it is removed (backport #7020 to release-7.1)

[sfc-gh-abeamon]

This is a backport of #7020.

It was previously possible for a team to be removed but for a relocate shard task to still have a reference to it. If that happened, the task would not detect when the team became unhealthy and could no longer be moved to.

Marking the team unhealthy signals to the relocate shard task that it should stop trying to relocate it.

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