How to use mutate in elasticsearch Input plugin?

Hi Experts ,

Requirement :- Remove fields from an existing Index.
I am using LS to reindex my data . I am using

input {
  elasticsearch {
hosts => ["localhost"]
port => "9200" 
index => "cef-2016-04-01"
scroll => "20m"
output {
  elasticsearch {
host => "localhost"
protocol => "http"
index => "cefoneshard"
  stdout {
    codec => "dots"

Above is working absolutely fine but I want to delete Message field from OLD index . By this I mean new index should not have message field in it . I was curious to know if this is possible with above LS config file .Something like Mutate. If not please help me to achieve this .


Mutate should definitely be able to do it.