Remember cbq isn’t expected to be a “simple unload” tool as you’re trying to use it here and note the help for -o does indicate that both the statement and results are written to the output.
To some extent what you can do depends on the version you’re using. In all versions you can turn off the signature and metrics with request parameters, but you’ll always have the request ID and status except if on 7.1+.
On 7.1+ you can add the “-terse” command line option to greatly reduce the non-result output. (Combine with turning off metrics & pretty printing for minimal output.) If you redirect the output rather than use -o you need only eliminate the “resultCount” line to capture just the results: