fix(shell-api): mongosh should throw an error when trying to drop a non-primary index MONGOSH-1608

[gagik]

test> response = db.test.dropIndex({"a": 1});
MongoshInternalError: can't find index with key: { a: 1 }

test> console.info(response);
{
  ok: 0,
  errmsg: "can't find index with key: { a: 1 }",
  code: 27,
  codeName: 'IndexNotFound'
}

mongosh seems to throw the error here instead of the dropIndex request going to the server. Hence response variable doesn't end up being set.