Remove BOLD-based databases for plant taxonomic classification with DADA2

[Sofokli5]

BOLD databases ('plantae-bold-its1' & 'plantae-bold-trnL') added with PR #883 included low quality sequences.
Removing these databases, after discussions within the METAPLANTCODE project.
Extra curation is necessary.

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[d4straub]

Oh thats a pity. Will you do the curation and add it later again?
PR looks good to me.

[Sofokli5]

Oh thats a pity. Will you do the curation and add it later again? PR looks good to me.

Most definitely!!