Remove redundant "seeds" tag

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• Fixes SimpleHarvest doesn't work with Sandwichable #35

My justification for this PR is two-fold.

1. Use of tags should be minimized as it pushes a standard that, in this case, really does not need to be applied. We can easily figure out which item is the seeds item by looking for an item that is a BlockItem, and comparing the resulting block from that item with the crop block.
2. An entire config file is already provided to the end user, which needs changing anyways if implementing modded blocks. Having two places in which the end user needs to do changing is redundant, especially considering point one.

If you're an end user and desperately want this change before it gets merged (or closed) I've published a release on my fork here