Decompresses the gzip file `source` into `dest`. If `dest` is omitted,
`source` must end in ".gz" and `dest` defaults to `source` with the
".gz" suffix stripped; if `source` does not end in ".gz" in that case,
the call fails and returns 0.
On success, the original `source` file is DELETED (unlinked); only the
decompressed `dest` file remains. Returns 1 on success and 0 on
failure. Both `source` and `dest` are subject to the driver's
read/write path validation (valid_read for `source`, valid_write for
`dest`); a rejected path causes the call to return 0.
For in-memory (non-file) decompression, use uncompress().