Menus now use the size that users have set globally for their
applications. This is accomplished by removing the fixed font size
definition (in points) for `QMenu` in `style.css`.
In some places the menus had been set to hard coded font sizes. This
code is also removed and applies to the following menus:
* Combo box menus
* Track operation widget (gear icon on tracks)
* The MIDI port menu
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