Remove ap-northeast-2 due to broken deploys

[reedobrien]

Please provide the following details to expedite Pull Request review:

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Description of change

Remove ap-northeast-2 from fallbackpublicclouds.{yaml|go}

Why is this change needed?
juju deploy fails there now and QA won't approve a PR adding google regions without removing this.

QA steps

1. Run the tests see them pass.

How do we verify that the change works?
Have QA validate the new fallback-public-clouds.yaml file.

Documentation changes

Possibly if we document the regions we support, but I think just calling juju update-clouds should fix things

Does it affect current user workflow? CLI? API?
N/A

Bug reference

https://bugs.launchpad.net/juju/+bug/1663047

Does this change fix a bug? Please add a link to it.