Fix Error 500s when loading repositories with license files
The licensee gem saves the license files in
/opt/gitlab/embedded/lib/ruby/gems/2.6.0/gems/licensee-8.9.2/vendor/choosealicense.com/_licenses/*.txt, which appears to have been
!3471 (merged). As a
result, loading a project that contained a valid LICENSE file would
return an error.
To fix this issue, we can prune the most space-consuming
vendor directories that
we don't need instead of removing them all.