Fix ASTERIXDB-1043
Fix ASTERIXDB-1043

The example for the index-drop statement was wrong. It only used a
Qualified name instead of a DoubleQualified

Change-Id: I762eadd60a7b9e09be244d8eaeb673dd03eb2108
Reviewed-on: https://asterix-gerrit.ics.uci.edu/514
Tested-by: Jenkins <d95b56ce41a2e1ac4cecdd398defd7414407cc08@fulliautomatix.ics.uci.edu>
Reviewed-by: Till Westmann <6a75d5097ecd0c0c685f0a2e96aeb5f14c655645@apache.org>

ecarm002/incubator-asterixdb,heriram/incubator-asterixdb,ecarm002/incubator-asterixdb,kisskys/incubator-asterixdb,apache/incubator-asterixdb,waans11/incubator-asterixdb,kisskys/incubator-asterixdb,ecarm002/incubator-asterixdb,kisskys/incubator-asterixdb,heriram/incubator-asterixdb,heriram/incubator-asterixdb,ty1er/incubator-asterixdb,waans11/incubator-asterixdb,ty1er/incubator-asterixdb,ty1er/incubator-asterixdb,heriram/incubator-asterixdb,kisskys/incubator-asterixdb,ty1er/incubator-asterixdb,ecarm002/incubator-asterixdb,waans11/incubator-asterixdb,apache/incubator-asterixdb,apache/incubator-asterixdb,kisskys/incubator-asterixdb,ecarm002/incubator-asterixdb,apache/incubator-asterixdb,apache/incubator-asterixdb,ecarm002/incubator-asterixdb,apache/incubator-asterixdb,kisskys/incubator-asterixdb,ecarm002/incubator-asterixdb,waans11/incubator-asterixdb,ty1er/incubator-asterixdb,waans11/incubator-asterixdb,kisskys/incubator-asterixdb,apache/incubator-asterixdb,heriram/incubator-asterixdb,waans11/incubator-asterixdb,waans11/incubator-asterixdb,heriram/incubator-asterixdb,ty1er/incubator-asterixdb,heriram/incubator-asterixdb