mtbl_info: Use mtbl_compression_type_to_str()
mtbl_info: Use mtbl_compression_type_to_str()

We now have an API function that converts an mtbl_compression_type value
to a human readable mnemonic. Use this instead of a long if/else if...
chain in mtbl_info when printing the compression algorithm.

rep/mtbl,rep/mtbl,rep/mtbl,farsightsec/mtbl,farsightsec/mtbl