/opt/cpanel/ea-php56/root/etc/php.d/local.iniSimilarly, you can find the local.ini file for any other version under /opt/cpanel/ea-php** folder.
Comment the line:
;extension=timezonedb.soOnce done, propagate the changes by remounting cagefs:
If it still doesn't work, you would need to reinitialize the cagefs with the following:
Once done, restart your apache, and should see the warning is gone.