It seems that you are using the scream extension. From the manual:
The scream extension gives the possibility to disable the silencing error control operator so all errors are being reported. This feature is controlled by an ini setting.
Scream is an extension for debugging that aims to display as many error messages as possible. This is done by ignoring the @
operator and always having the highest error_reporating level available. (regardless of your error_reporting
setting). So you will have to deactivate the extension in your php.ini:
scream.enabled = off
BTW: I would not update a server having 170 websites with code errors. It's a ticking bomb now. It would be better to migrate them site by site to the new PHP version. Maybe having two servers parallel during the migration process.