[FEAT]: Return `RepositoryContentChangeSet` from `RepositoryContentsClient.DeleteFile`

[dylanlerch]

Describe the need

The CreateFile and UpdateFile methods in RepositoryContentsClient return a type of Task<RepositoryContentChangeSet>, but DeleteFile does not (it only returns Task).

The delete a file endpoint returns the same response structure as the create or update file contents endpoint (with null content), so the DeleteFile methods should also return Task<RepositoryContentChangeSet>.

SDK Version

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API Version

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Relevant log output

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