DEV: Remove SiteSetting.s3_force_path_style (#7210)

- s3_force_path_style was added as a Minio specific url scheme but it has never been well supported in our code base.
- Our new migrate_to_s3 rake task does not work reliably with path style urls too
- Minio has also added support for virtual style requests i.e the same scheme as AWS S3/DO Spaces so we can rely on that instead of using path style requests.
- Add migration to drop s3_force_path_style from the site_settings table

db/migrate/20190320104640_remove_s3_force_path_style.rb

@@ -0,0 +1,9 @@
+class RemoveS3ForcePathStyle < ActiveRecord::Migration[5.2]
+  def up
+    execute "DELETE FROM site_settings WHERE name = 's3_force_path_style'"
+  end
+
+  def down
+    raise ActiveRecord::IrreversibleMigration
+  end
+end