$re = '/{"eventType":"delete","ServerSerial":"0","ServerName":""[^}]+},?/m';
$str = '{"eventType":"delete","ServerSerial":"1556562030","ServerName":"XYZ_U_O","deletedat":"2018-08-24 17:56:39.974"}
{"eventType":"delete","ServerSerial":"0","ServerName":"","deletedat":"2018-08-24 17:56:34.944"}';
$subst = "";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php