IPFS: remove special handling for CBOR nodes

[djdv]

Extracted from: #27 (comment)

We probably don't have to handle non-UFS nodes.
Any non-UFS node can just be handled as a binary blob that sources data from the node's blocks.

Previously we had an option to return cbor data as JSON, but this was removed, and the special handling as a cborFile probably doesn't need to exist anymore.
This kind of behaviour is better emulated at the system level.
I.e. cat /the/cbor/node | cbor-formatter