Other than removing a redundant action, we're fixing two bugs when
blocking an author using the links in the public views:
* We were always redirecting to the debates index, even if we blocked
the author of a proposal or an investment
* We weren't showing any kind of success message
In theory it's possible to add a `host` parameter to a URL, and we could
end up redirecting to that host if we just redirect using query
parameters.
Generating the path using `url_for` with `only_path` solves the issue.
Note in the tests I'm using the `get` method because the `patch` method
wouldn't send query parameters. This doesn't mean the action can be
accessed through GET requests, since controller tests don't check route
verbs. Using feature specs doesn't seem to work because `controller` and
`host` parameters are filtered automatically in feature specs.
Also note I'm not testing every hidden/moderation controller because
they basically use the same code.
