[libc++][format] Updates LWG3462 status. (#80550)

The specifications of format had a contradiction, libc++ always
implemented the code as-if LWG3462 has been done; the contradiction was
a bit hard to spot.

Marks as nothing to do:
- LWG3462 ยง[formatter.requirements]: Formatter requirements forbid use
of fc.arg()

NOKEYCHECK=True
GitOrigin-RevId: e1da74d916e58f3c7748c21757cba1922aecbc52
1 file changed