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.
I'm guessing we shouldn't use more than 1 thread here since we are only removing < 10 rows...where is the numThreads generally pulled from. It may be OK to make this 1