Remove Indexes on MongoDB

[
   {  "v" : 1,
      "key" : { "_id" : 1 },
      "ns" : "test.pets",
      "name" : "_id_"
   },
   {
      "v" : 1,
      "key" : { "cat" : -1 },
      "ns" : "test.pets",
      "name" : "catIdx"
   },
   {
      "v" : 1,
      "key" : { "cat" : 1, "dog" : -1 },
      "ns" : "test.pets",
      "name" : "cat_1_dog_-1"
   }
]

db.pets.dropIndex( "catIdx" )

db.pets.dropIndex( { "cat" : -1 } )

References
https://docs.mongodb.com/manual/reference/method/db.collection.dropIndex/#db-collection-dropindex