Phase-out of symbolic icons

[palob]

This is more of an announcement than an issue. I am going to remove as many as possible symbolic icons from Numix (16px X 16px size, stored in scalable, named *-symbolic, monochrome or oligochrome designs).

Now that Numix's bus factor is 1 I am looking for ways to improve maintainability, to shed ballast.
I think there's very little leeway for a distinct Numix design with symbolic icons. Symbolic icons inherited from other sources blend in just as well.

More discussion in #1404.

This is the place to raise negative effects I might have overlooked.

[palob]

I'll probably keep scalable/mimetypes, scalable/places and scalable/status.

I also won't remove *-symbolic icons in 22and 24. Might be needed in those sizes or aren't supposed to be there, I don't know.

[palob]

As an aside, at least for GNOME it appears a light theme is not needed anymore, symbolic icons are reverted automatically.