Fixes#22524.
This affects both the banner in the main compose box and the banner
in the message edit compose box. The use of ProgressBar has been
replaced with a more simple CSS (with light Javascript) solution.
The classnames are changing because the upload banner is now a
template rendered and remove()-ed from a banner container
(#compose_banners in the composebox, and a new div for banners in the
message edit view). It used to be in the send_status container so
there are a lot of class renames across the codebase.
This is part several updates for #22524.
This commit also removes `compose_error.hide()` since there is only
one remaining use of it (which has been replaced by the contents of
`hide()`). Eventually `#compose-send-status` should be replaced
fully in a future PR, after we rewrite the upload banner to use
the new banner template.
Testing note: I removed the test test_compose_not_subscribed_clicked
since it heavily relies on the old way of rendering banners and is too
UI-focused (instead of logic focused) for me to feel like it's worth
testing that the banner is removed when clicking the button.
