Two "Configure" actions in the Audio applet

The one right on the header opens the applet's own settings page which has several options listed in it that are actually global options, not per-applet options.

Inside the hamburger menu is another settings action which opens the KCM.

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We should delete the applet-specific settings page because everything in there is global in scope, and move them into the KCM. Then the action on the header can be used to open the KCM, which will make the hamburger menu disappear since its' single remaining action will be displayed as a button instead.

See https://bugs.kde.org/show_bug.cgi?id=440846 and https://bugs.kde.org/show_bug.cgi?id=443356