[tex-k] Typos in METAFONT's help messages

[胡亚捷 (Hu Yajie)]

I mistakenly thought "use" couldn't apply to declarations and commands,
but it turns out that The METAFONTbook has such collocations:

l. 5874
The program for `(' uses a ^@filldraw@ command, which we haven't
l. 10884
\ (You probably should use the @message@ command first, to give the
l. 18315
|and you can use ordinary TeX commands (e.g., to \input a file).}}}|

So...please drop this one.