MFC r291377: vidfont: with vt(4) omit size from vidcontrol -f

MFC r291377: vidfont: with vt(4) omit size from vidcontrol -f

When using syscons, vidfont extracts the font size from the filename
passes it to vidcontrol -f. In vt(4) mode the size argument is not
required, and some of the fonts in /usr/share/vt/fonts do not have the
size in the filename, which caused vidfont to fail. Thus, just omit the
size argument in vt(4) mode.

git-svn-id: svn://svn.freebsd.org/base/stable/10@293335 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f