We currently have a specific REST action to retrieve all aliaes, which
uses internally the get index API. This doesn't seem to be required
anymore though as the existing RestGetAliaesAction could as well take
the requests with no indices and aliases specified.

This commit removes the RestGetAllAliasesAction in favour of using
RestGetAliasesAction also for requests that don't specify indices nor
aliases. Similar to elastic#31129.

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