fix drop search index example (#141)

(cherry picked from commit 5babfca)

Author: stephmarie17

source/includes/indexes/indexes.py

@@ -175,5 +175,5 @@
 # end-update-vector-search-indexes
 
 # start-delete-search-indexes
-collection.drop_index("my_index")
+collection.drop_search_index("my_index")
 # end-delete-search-indexes