Remove the dependency on snappy

[judah]

Our bindings currently link against the snappy C library due to the dependency on snappy-framing. As far as I can tell, the only reason we use that library is for Data.Digest.CRC32C which is pure Haskell code and doesn't actually use that C dependency.

The snappy and snappy-framing packages are also currently not in Stackage, which prevents tensorflow-records and tensorflow-records-conduit from being there as well.

As suggested in the code, one option is to split out the crc32c functionality into its own package.