Revert "require https for external links"

This reverts commit bb0bb92.

Remove actual test for now, as it causes failures in CI, where github.com links get generated as http

Eventually this should be fixed with github/pages-gem#611 or similar

Rakefile

@@ -14,7 +14,6 @@ task :test do
   Rake::Task['spec'].invoke
   HTMLProofer.check_directory('./_site',
                               check_html: true,
-                              enforce_https: true,
                               validation: { ignore_script_embeds: true },
                               url_swap: { %r{https://choosealicense.com} => '' },
                               hydra: { max_concurrency: 10 },