amd64 GENERIC: Drop hints for fdc0 and ppc0

Modern x86 systems do not ship with ISA floppy disk controllers or LPT
ports.

Reviewed by: imp
Differential Revision: https://reviews.freebsd.org/D45946

(cherry picked from commit 480cc750a2a8f92d078803f15eecb1f8a084a1ea)