fix: make go-licenses work better with the embed package

[jimmale]

As per discussion in #79 , go-licenses with the --force option currently deletes the output directory before loading the packages. If the output directory is embedded in the application with the embed.FS package, this results in compilation (and by extension, loading) to fail, which in turn causes go-licenses to fail.

This PR swaps the order of operations (as recommended by @wlynch) so that the output directory is deleted after go-licenses has already collected the licenses.

The use case for this is to embed all of the licenses of a golang application's dependencies in the golang application itself, so that they can later be retrieved. For example, by a --license CLI argument or something similar.

[wlynch]

Thanks! 🎉

[n3wscott]

This PR has introduced a bug where when you run the tool on an existing repo with the output directory in the project being scanned, https://github.com/google/go-licenses/pull/90/files#diff-63d2514e96da76ad8bd5c2460f4ea67c0a6c6ba1055a8890b7ec0c686bcc183fR70 finds all the previous license, which then are not locatable after https://github.com/google/go-licenses/pull/90/files#diff-63d2514e96da76ad8bd5c2460f4ea67c0a6c6ba1055a8890b7ec0c686bcc183fR76 if you use the tool with the the --force flag in play.