META_MODE: Remove unneeded groff/tmac special GENDIRDEPS_FILTER.

This is converting the path usr/share/tmac.*stage to something else, but
nothing ever installs or reads from such a path. They might look in
stage.*usr/share/tmac, but that's not what this is matching. Additionally
the .dirdeps match all of the tmac files back to gnu/usr.bin/groff/tmac
fine.

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