As the error states your declaration needs to be compatible with the class you're extending. This means that functions needs to have same number of properties passed.
The original class
Mage_ImportExport_Model_Export have method
export() but it doesn't receives any parameters. In your class your method has an extra parameter
$destination. Remove the parameter from method definition and the error will be resolved.
On the other hand it looks like you're doing this wrong. You're not using Magento module concept, and you're declaring multiple classes in one file which AFAIK will fail to autoload in PSR-4. You really should do this as a module, not a file in public place where it'll be available for everyone.