remove var keyword in WC_Integrations
remove var keyword in WC_Shipping
remove var keyword in WC_Shipping_Method
remove var keyword in WC_Email_Customer_Invoice
remove var keyword in some email classes
remove var keyword in WC_Email_Customer_Reset_Password
remove var keyword in WC_Shipping_International_Delivery
remove var keyword in WC_Product_Cat_Dropdown_Walker
remove var keyword in WC_Product_Cat_List_Walker
Merge pull request #6963 from bryceadams/patch-6962

Removal of old PHP class var use