This commit removes the unnecessary `data-list-widget` attribute
present in the <div> and <tbody> tag for muted_topics and muted_users table.
It became unnecessary/useless in 19cf6d0e04 and
then was renamed while still useless.
Also uses the correct variable name `muted_topic` and `muted_user`
instead of `muted_topics` and `muted_users` to render a item of their list
in DOM through Listwidget.