usbdevs2h: Ignore First Line and stop generating $FreeBSD$

Just ignore the first line of the usbdevs file. And stop recording what
the usbdevs* files were generated from. It's said '$FreeBSD$' for years
now...

Sponsored by: Netflix

(cherry picked from commit 94b73d30ef2b0d85d4834a1e4dc29e0457a8faef)