This commit removes `oss` storage driver from distribution as well as
`alicdn` storage middleware which only works with the `oss` driver.
There are several reasons for it:
* no real-life expertise among the maintainers
* oss is compatible with S3 API operations required by S3 storage driver
Signed-off-by: Milos Gajdos <milosthegajdos@gmail.com>