public <E extends Element> void dropIndex(final String key, final Class<E> elementClass) {
        if (Vertex.class.isAssignableFrom(elementClass)) {
            if (null != this.vertexIndex) this.vertexIndex.dropKeyIndex(key);
        } else if (Edge.class.isAssignableFrom(elementClass)) {
            if (null != this.edgeIndex) this.edgeIndex.dropKeyIndex(key);
        } else {
            throw new IllegalArgumentException("Class is not indexable: " + elementClass);
        }
    }
Drop the index for the specified element class ({@link Vertex} or {@link Edge}) and key.

@param key          the property key to stop indexing
@param elementClass the element class of the index to drop
@param <E>          The type of the element class
tinkergraph-gremlin/src/main/java/org/apache/tinkerpop/gremlin/tinkergraph/structure/TinkerGraph.java