vt: Remove FONT specification from INDEX files

There is no reason to change the font in order to select a keymap or a
font.

This was done in the syscons(4) era to ensure that a font with the
appropriate character set was used for kbdmap or vidfont's localized
menu, but vt is always UTF-8 and this is no longer necessary.

PR: 235565
Reviewed by: imp
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D51640

(cherry picked from commit bf426b859bda58a1d6598bb9516ffc6692b2502f)