You can disable the elastic search from the cmx server properties file.
You can refer to the KB : 564677 for more information on how to configure elastic search. you can back trace the conf. from the KB
To disable Elastic search, you would need to do the following:
1) Stop elastic sever
2) comment out the newly added properties as per the above KB from properties cmxserver.properties and from cmxcleanse.properties.
3) Change the cmx.ss.enabled back to false.
4) Remove the Esnode created on provisioning tool through "Infrastructure settings".
We do not have to change any property just cmx.ss.engine=false in both cmxserver.properties and cmxcleanse.properties and re-start the application server. It should disable your smart search.
In addition to Harsha's recommendation, ensure that you have disabled search processing for all the registered Proecss Servers for all the ORSs. Remember that all ORSs will maintain individual ORS list in C_REPOS_CLEANSE_MATCH servers so ensure that it is disabled individually from all the ORSs.