Remove any usage of the Arial font and similar

[afercia]

Here and there in the components, the font Arial is used especially in the snippet preview form labels, fields, and buttons but also for other elements. See for example #568

This is probably a leftover. Arial shouldn't be user at all, unless I'm missing something. Worth reminding WordPress uses native fonts faces, meaning it lets the application inherit from the operating system default fonts.

Here's some of the Arial font stacks used in yoast-components:

font-family: arial, sans-serif;
font-family: Arial, Helvetica, sans-serif;
font-family: Arial, Roboto-Regular, HelveticaNeue, sans-serif;