GEOMESA-191 Implement deleteSchema for featureType

deleteSchema removes both metadata and the 3 tables per feature type. Also
checks to see whether or not it's an older 0.10.x table, and if so, uses
the AccumuloFeatureWriter's remove() function to remove rows from the table.
Interestingly enough, I was getting the correct behavior -- the 'if' should check whether or not we are using a post-0.10.x table or not. But it seems like we definitely shouldn't be able to read the metadata if it's been deleted. I've moved deleteMetadata to the end of the deleteSchema function and will re-commit.