Obsolete icons
I was looking through the icons and noticed that some of them are obsolete as in the referenced website or service does not exist anymore.  This may be an incomplete list.

* src/icons/svg/google-plus.svg
* src/icons/svg/google-plus-official.svg
* src/icons/svg/google-plus-square.svg
* src/icons/svg/stumbleupon.svg
* src/icons/svg/stumbleupon-circle.svg
* src/icons/svg/vine.svg

Does anyone else know of any more that could be removed?

Would the removal process simply be to delete the files and remove their references in `src/icons/.fontcustom-manifest.json` and `src/icons/icons.yml`?