Remove zstandard dependency in favor of numcodecs

[normanrz]

I added zstandard as a dependency because the zstd in numcodecs doesn't expose the checksum config. This will be introduced in https://github.com/zarr-developers/numcodecs/pull/519. Once that PR is merged, we can use the numcodecs version.

[mkitti]

The correct default level should be 0 which will then allow the Zstd C library to use the default setting according to how it was built: https://github.com/facebook/zstd/blob/97291fc5020a8994019ab76cf0cda83a9824374c/lib/zstd.h#L338

[normanrz]

Now that numcodecs 0.13 is out, we can move forward with this.