Fix 1st col of nouns.6forms.csv

The first column of nouns.6forms.csv is now unique and contains less parallel forms.
This makes the file easier to process.

The new file was obtained by running it through the vabamorf synthesizer:

    cat nouns.6forms.csv | sed "s/,.*//" | tr '|' '\012' | uniq | java Synth

where Synth is a currently unpublished commandline tool that uses vabamorf to
synthesize noun forms.

About 10 duplicate lines were removed manually. (Didn't want to sort|uniq as
this would have rearranged too many lines. At some point we should apply
"LC_ALL=et_EE.utf8 sort" though.)