We now use micromodal in the license update modal on billing page
to make it consistent with other modals in the app and this is
preparatory work for moving away from bootstrap as well.
Previously this was only available on the upgrade page - meaning an
organization that already bought a plan wouldn't be able to request a
sponsorship to get a discount or such, even if qualified.
This lets us simplify the long-ish ‘../../static/js’ paths, and will
remove the need for the ‘zrequire’ wrapper.
Signed-off-by: Anders Kaseorg <anders@zulip.com>