generate_bom: Fix the JSON syntax of the licensing report

When not using the --preatty flag the script produced malformed JSON as it directly printed the Python dict representation rather than properly serializing it. The most visible issue is that this results in single quotes being used rather than the double quotes required by the JSON spec.

Drop make the "pretty" formatting the default and drop the --preatty flag, which also "fixes" the typo. :D

The size overhead of the indented JSON is not much of a concern given that we're gzipping the result anyway.