make/doc-i18n-root-rules.make: grep --label=""

[Matthias Kilian]

There are two make rules using a command like

        find $(outdir)/$* -name '*.html' |
        xargs grep -L --label="" 'UNTRANSLATED NODE: IGNORE ME' | ...

What's the reason for that `--label=""'? It's breaking the build
with OpenBSDs native grep (in /usr/bin/grep), and I don't see any
difference when using GNU grep with and without --label="", so I'd
like to just drop that option.

Ciao,
        Kili