x11-fonts/iosevka: Update to 6.0.1

This commits switches the port from using TTF files to using TTC files.
As a result, the default package is no longer over 4 GB,
but 1.6 GB instead. The downside is that options of the port are less
granular now.

Changes: https://github.com/be5invis/Iosevka/releases/tag/v6.0.1