gandi.cli: remove

[branchvincent]

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This is the last formula that has a runtime dependency on python-setuptools, which we might not keep (#167905)

We disabled it 7 months ago and only has 29 installs in the last year, so let's just remove it:

$ brew info gandi.cli
# ...
install: 0 (30 days), 0 (90 days), 29 (365 days)

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